Neutral Citation Number: [2013] EWHC 738 (Ch)
Case No: NE01722
IN THE HIGH COURT OF JUSTICE
CHANCERY DIVISION
NEWCASTLE UPON TYNE DISTRICT REGISTRY

Date: 10/04/2013

Before:
MR JUSTICE BRIGGS
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Between :

	(1) COLIN BAINBRIDGE WILLIS
(2) AVRIL WILLIS	Claimants	
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	DERWENTSIDE DISTRICT COUNCIL	Defendant	

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Mr Christopher Knox (instructed by Bennett Richmond Solicitors) for the Claimants
Mr Howard Smith (instructed by DWF LLP) for the Defendant

Hearing dates: 19, 20 March 2013
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Judgment

Mr Justice Briggs : 
Introduction
1.	This is a claim for damages in nuisance, negligence and under the rule in Rylands v Fletcher arising from the escape of CO² gas from land owned by the former Derwentside District Council at Hamsterley Colliery, in the county of Durham.  The claimants Colin and Avril Willis are the owners of property consisting of a house and garden known as Derwentside House, Low Westwood, Hamsterley (“the Property”).  They also occupy adjacent land, including two barns, as licensees of the Council, which they use as a smallholding for the breeding and rearing of animals and poultry.
2.	The Property lies on the southern flood plain of the River Derwent.  Immediately to the south of the Property there is rising ground within which lie extensive coal seams forming part of the West Durham coalfield, together with extensive disused underground coal workings.
3.	Immediately to the south of the garden of the Property, roughly in line with its western boundary, lies the mouth of a disused drift or adit known as the Burn Drift, which runs south south-east under the Newcastle Road until it connects with the disused Hamsterley colliery workings.  The mouth of the Burn Drift lies on land acquired by the council from the National Coal Board in January 1978.  
4.	For many years before it was sealed in 2006-7, the mouth of the Burn Drift was open to the air, access to it being obstructed only by an iron barred grille and undergrowth.  Since it lies at the lowest part of the disused workings, the Drift formed a natural point of egress for CO² generated by un-worked and partly worked coal seams and residues within the workings.  The effect of that natural reaction is to convert oxygen into carbon dioxide, giving rise to an atmosphere within the workings of depleted oxygen and increased carbon dioxide, known locally as black damp or stythe gas.  Although not poisonous (like carbon monoxide) or explosive (like methane), the combination of reduced oxygen and increased carbon dioxide can cause loss of consciousness and asphyxiation in humans, animals and birds.  Although stythe gas is likely eventually to disperse in the open air, particularly if there is any wind, its heavier than air CO² content means that, in still conditions, it may accumulate close to the ground in dangerous concentrations, both in the open air, and in unventilated or poorly ventilated buildings.
5.	Ground investigations carried out in 2006 with a view to construction of a care home on land above the Burn Drift, lying between the Drift mouth and the Newcastle Road, led to the discovery that in certain atmospheric conditions large quantities of stythe gas were being emitted from the mouth of the Burn Drift.  Investigations by the Coal Authority revealed that these emissions gave rise to dangerous levels of CO², together with oxygen depletion, in the immediate vicinity of the mouth of the Drift.  Further studies revealed significantly high (albeit not immediately dangerous) levels of CO² within the Willises’ house on the Property (“the House”). As a result of what was perceived to be an unacceptable risk to their safety, the Willises and their family were evacuated from the House at the end of July 2006.  At their request (due to their wish to provide full-time care for their livestock) they were accommodated (for sleeping purposes) first in a caravan then in a portakabin at the Property, while temporary measures were undertaken to reduce the gas emissions to a safe level.  Measurements within the House led to their resuming full-time occupation in it at Christmas 2006.  Meanwhile, an expensive programme of permanent remedial works was undertaken for the purpose of eliminating those risks, which were completed during 2007.  Those works have, thus far, been successful in preventing any further gas emissions from the mouth of the Drift on to the Property, save at a negligible level giving rise to no relevant risks or impairment of its reasonable use and enjoyment.  The works consisted of a gas ventilation and revised water drainage scheme, costing in excess of £150,000, designed, commissioned and supervised by the Coal Authority but paid for by the Council.
6.	Nonetheless the Willises seek compensation for losses incurred by them in connection both with the emissions and the remedial works under the following four broad headings:
(1)	They say that the uncontrolled emissions prior to the end of July 2006 constituted a nuisance (or a Rylands & Fletcher escape) which caused the death by asphyxiation of animals and poultry kept by them at the Property and the adjoining smallholding occupied by them under licence, as well as causing them headaches and mild discomfort.
(2)	They say that the defendant delayed dealing with the discovery of escaping stythe gas in April 2006, while squabbling with the Coal Authority as to the apportionment of responsibility, so that the remedial steps once taken caused unreasonable disruption, distress and inconvenience to them, until completed in 2007.
(3)	They say that a tight-fisted refusal by the Council to reveal or explain the nature and causes of the gas emissions, or the thinking behind the design of the remedial scheme, led them to have to incur substantial expense in the appointment of their own mining expert to advise them.
(4)	Most importantly (in terms of value) they say that the failure of the Council to obtain or make available a certificate of the due completion of the remedial scheme, or to conduct monitoring or maintenance of the remedial works in accordance with the Coal Authority’s recommendations thereafter, mean that the Property is both un-mortgageable and un-saleable, and will remain so for the indefinite future, so that they have suffered a complete loss of its capital value, estimated at some £200,000.
7.	The Council denies any monetary or other continuing liability to the Willises.  In outline, they say that prior to mid-2006 there was nothing to make them aware of gas emissions from the Burn Drift, let alone at a level sufficient to give rise to a danger of asphyxiation to anyone on the Property.  Thereafter they say that any risk of nuisance was abated by a proper scheme of remedial works which, regardless of any imperfections in subsequent monitoring, will satisfactorily protect the Property for the indefinite future.  Further they say that the emission of stythe gas from the disused coal workings into the House came not from the mouth of the Burn Drift on their land, but from an underground pipe which drained the Drift at a point south of their land, into a manhole or sump under the House, for the operation of which as a conduit for gas they cannot be held liable, even though the pipe passed through their land on the way.  In relation to the four heads of loss claimed by the Willises, the Council say:
(1)	There is no evidence to show that the deaths of animals and poultry were caused by asphyxiation, still less at a time when the Council ought to have appreciated that there was a potentially dangerous emission of stythe gas from the mouth of the Drift.
(2)	Although the evacuation and remedial works undoubtedly caused discomfort and inconvenience to the Willises, this was no more than the ordinary consequence of the abatement of a potential nuisance, for which no liability lies in damages.
(3)	There was no need for the Willises to employ their own expert, since the remedial works were being designed, commissioned and supervised by the Coal Authority.
(4)	Since the Council has abated any possible nuisance, there can be no liability for any consequence in terms of capital value of the absence of a completion certificate for the remedial works, or for any defects in on-going monitoring and maintenance.  Furthermore, the remedial works will sufficiently protect the Property even if not monitored or maintained.
8.	The legal and forensic examination of these issues over three full days (not including pre-reading or judgment writing) will, unfortunately, probably have involved effort and expense broadly equivalent to the remedial works themselves. [For reasons which will appear, that effort and expense ought to have been avoidable.  It would have been avoided if the Council had adopted a less doctrinaire attitude to its legal responsibilities and a more careful approach to the monitoring and maintenance of the remedial works after their completion in 2007.]
The Evidence
9.	The physical characteristics of the locus in quo including the Burn Drift and the relevant drainage systems were all satisfactorily depicted on helpful large scale plans and with the assistance of photographs.  The relevant conveyancing history was also fully documented.  Furthermore, the conduct (mainly by the Coal Authority) of the investigation, design, commissioning and supervision of the remedial works was also well-documented by surviving contemporaneous emails and, in particular, by a series of successive monthly reports by the Coal Authority.
10.	Mr and Mrs Willis and their son Christopher each gave vivid evidence, in part backed up by diary notes, of the unpleasant experience of being, first, evacuated and then surrounded by substantial engineering works for the best part of a year.  They were, understandably, unable to give reliable evidence about the timing of the death of various of their animals and poultry, save for a litter of puppies, most of whom appear to have died between April and the end of July 2006 while the gas emission was being investigated, but before any remedial works began.  They were, understandably, unable to produce veterinary evidence of cause of death (which would in any event probably have involved disproportionate expense), or of the cause of headaches and heart ailments which they each suffered thereafter.   I found the evidence of Mr and Mrs Willis and their son to be honest and generally reliable, although Mr Willis had a very poor recollection of dates or timings, his oral evidence as to the dates of death of his various animals and poultry being wholly at variance with the written evidence of both himself and his wife in that respect.
11.	The documentary evidence of the Council’s response to the discovery of the gas emissions, the undertaking of responsibility for the remedial works and their subsequent monitoring and maintenance was, at best, patchy.  It was marred by what appeared to have been unrealistic claims to privilege by reference to a supposed dispute with the Coal Authority as to liability for the works, and by the apparent loss of the files of Mr George Cansino, the Principal Valuation and Estates Manager of the Council, who assumed primary executive day to day responsibility for the Council’s response to the emissions, once discovered.  The result was that relevant documents emerged in dribs and drabs and continued to do so during the trial.  To some extent the Council’s difficulties may have been exacerbated by the fact that it was dissolved in 2009 and its affairs taken over by way of merger into the Durham County Council.  
12.	As for witnesses, the Council called Mr Cansino himself, Ms Theresa Morgan, its risk officer, who had played a day to day role in the monitoring of the remedial works after 2007, but without being in managerial charge, and a Mr Andrew Cowan, who personally carried out minimal monitoring of the remedial works in 2012 and 2013 as an employee of Premier Waste Management Limited, at the Council’s direction.
13.	The evidence of Mr Cowan and Ms Morgan was reliable, but of marginal relevance.  Mr Cansino retired from the Council in 2009.  It is no criticism of him that his recollection (in particular of a relevant meeting held in late January 2008) was less than perfect.  He was hampered by the apparent disappearance or retention on grounds of privilege of his relevant file, and by a rather wooden attitude to aspects of the history about which, during cross-examination, his conduct was criticised.  Nonetheless I had no concerns as to his honesty.
The Expert evidence
14.	The claimants called Mr Norman Jackson.  After a career within British Coal which gave him very substantial experience in the practicalities of mine closure, gas and water issues arising from coal workings, he had been a management and mining consultant as a sole trader from February 1995.  It was he to whom the Willises had recourse as an expert adviser about their problems in and after 2006.
15.	Mr Jackson was a straightforward, independent, highly experienced and articulate witness with determined views about the matters in issue.  The basis for his views was practical rather than academic.
16.	The Council called Professor Paul Younger, from Newcastle University, by profession a hydrologist and mining environmental engineer.  Professor Younger’s qualifications were more academically than practically based.  He was better qualified by his studies than was Mr Jackson in relation to the particular matters about which they differed, which related mainly to the extent to which gas and water might pass horizontally through strata (including strata disturbed by man-made works).  He was again a clear, articulate and helpful witness.  He showed no disabling partiality towards the Council.  Nonetheless, in cross-examination he did tend to demonstrate a surprisingly defensive and, at times, unreasoning tendency to adhere rigidly to previously formed views, which detracted a little from the authority which his otherwise commanding range of academic expertise might otherwise have given him.  
17.	One thing about which both Mr Jackson and Professor Younger did agree was the high quality generally to be found in the Coal Authority’s own approach to the investigation and remedying of risks arising from disused coal workings.  The result was that, although their writers were neither identified nor called to give evidence, it was possible for me to place considerable reliance, as written expert evidence, upon the contemporaneous reports carried out by the Coal Authority, and the gas measurements taken during the initial investigation of the gas emission in June and July 2006, and during the carrying out of the remedial works thereafter.  Those consecutive reports illustrated the stage by stage development in the Coal Authority’s understanding of the causes of the stythe gas accumulations on the Property.  Even though Professor Younger did not always agree with their conclusions, I found them to be of particular value.
The Facts
18.	Prior to 1960, by which time active coal mining at the Hamsterley colliery had ceased, the Property had been a pumping station, designed and built for pumping water emerging from the Hamsterley mine workings to the Consett Ironworks, some two miles to the east.  One source of the water consisted of a clay pipe laid from the lowest point in the Burn Drift, a little south of the Council’s land, underneath the Drift, past its mouth, and terminating in a sump underneath the House.  From there, a further clay pipe system provided a means of drainage northward to the River Derwent.  The relatively modest discharge along that pipe (not exceeding about 1.5 litres per second when recently measured) suggests that this may not have been the only source of water to the pumping station, and the dimensions and precise positioning of the sump have never been ascertained.
19.	From its lowest point (in local parlance a swallow) the Drift trends gently up hill both northward to its mouth and southward to the coal workings.  The swallow is therefore the natural collecting point both for water leaking or percolating into the Drift, and for CO², following the cessation of mechanical ventilation within the mine workings.  Since the rate of water flow along the pipe between the swallow and the House was insufficient  to occupy the whole diameter of the pipe, (at least after water levels stabilised following abandonment of the workings),  there was a propensity for stythe gas to pass along that pipe system from the swallow to the House.
20.	The House was separated from the Coal Board’s ownership of the Hamsterley Colliery and surrounding land by a conveyance dated 23 July 1960.   Clause 3(1) excluded any liability of the Coal Board to make good or pay compensation for damage or loss caused directly or indirectly by any mining operations under or adjacent to the Property, before or after the date of the conveyance.  Clause 1 and paragraph 1 of the Second Schedule reserved to the Coal Board all mines, beds and seams of coal and other minerals under the Property together with “any building structure or works now or hereafter erected, constructed or placed on or in the said land”.  On its true construction this reservation appeared to be limited to building structures or works necessary for the searching, winning, working, getting and carrying away of coal or other minerals.
21.	From 1960 the House appears to have been occupied as a residential dwelling by a succession of owners, until conveyed to Mr and Mrs Willis on 26 June 1978.  This was a little over five months after substantial parts of the land in and around the Hamsterley colliery were transferred by the Coal Board to the Council by conveyance dated 13 January 1978 (“the 1978 Conveyance”).  This included land on all sides of the Property so that it became, in effect, an island within land acquired by the Council, accessible by a right of way from the nearest public highway.  That part of the Burn Drift lying immediately to the south of the Property, including its mouth, was expressly included within the 1978 Conveyance.  By clause 2 and paragraph 1 of the Fourth Schedule the Council covenanted at its own expense to fill in “the Shafts and Drifts in a manner approved by the Vendors to the level of the land surrounding the Shafts and the drifts and thereafter maintain the fillings to that level”.  That covenant applied to the Burn Drift and to a number of other shafts and drifts identified on Plan C annexed to the 1978 Conveyance.  Another of them was the Church Drift, the entrance of which lay a short distance to the southwest of the Property, between it and the local church, in an area of woodland.
22.	By paragraph 2 of the Fourth Schedule the Council undertook to keep the Coal Board indemnified against any liability and expense in any way related to the shafts and drifts or their fillings which had not been occasioned by any mining operations carried out by the Coal Board after the date of the conveyance.
23.	Neither the Burn Drift nor the Church Drift was filled in by the Council pursuant to the covenant to do so in the 1978 conveyance.  By 2006 the Burn Drift was, as I have described, closed off only by an iron grille.  The Church Drift remained open and had been used, to some extent, for dumping.  There is no evidence, documentary or otherwise, that this failure to deal with the two drifts as required by the 1978 Conveyance had been the subject of complaint, either by the Coal Board or anyone else, including the residents from time to time at the House.
24.	By 2006 Mr and Mrs Willis and their family had established several activities at the Property and on the neighbouring smallholding held on licence.  These included a haulage business and the keeping of pigs, horses, ducks, hens, cats, dogs and even swans.  Mrs Willis also bred and showed boxer dogs.
25.	Prior to 2006 nothing led the Willises to suspect that the Property and the adjacent barns were affected in any way by gas escape from the Burn Drift.  Nonetheless, Mr Jackson and Professor Younger were agreed, and I so find, that stythe gas had in fact been crossing the boundary between the Council’s land around the Burn Drift and the Property for many years, broadly in the pattern discovered by the Coal Authority during 2006, before remedial measures were taken.  I shall explain that pattern in more detail when describing those investigations.  For present purposes it is sufficient to say that nothing in what the Coal Authority discovered in 2006 suggests that anything had recently occurred to create such a pattern of gas emissions for the first time.  
26.	The build-up of stythe gas in disused coal workings begins once active ventilation is switched off.  Its emission from those workings into the atmosphere is frequently triggered by the rise in water levels occasioned by the discontinuance of pumping.  At the Hamsterley colliery, the workings had been disused since, at the latest, 1960 and the water table had reached equilibrium years before the Willises and the Council acquired their respective parts of the relevant land in 1978.  There is no evidence that other relevant physical or geographical changes occurred between 1978 and 2006 which might suggest that the pattern of gas emissions then discovered was of recent origin. 
27.	Risks arising from gas emissions from the Burn and Church Drifts came to the Coal Authority’s attention in April 2006, as the result of investigations carried out in connection with the development of a care home to the south of the Property.  By the end of April it had been reported to Mr Cansino at the Council by telephone that the Burn Drift was “emitting dangerously high levels of CO², 10%. This will asphyxiate anyone who enters the opening or stands too close”.  Emissions from the Church Drift were reported at lower levels, but still regarded as giving rise to a potential risk.  The report to the Coal Authority warned of a risk of potential harm to the Willises’ animals, but it is not clear that this was passed on to the Council.
28.	A more detailed written report by email (with attached photographs and data) from a Mr Olivant of the Coal Authority to Mr Cansino at the Council on 22 June 2006 warned of stythe gas layering on the floor of the cutting containing the Church Drift as far as 25 metres from its mouth and of persistent CO² levels at the mouth of the Church Drift between 5% and 8% for 20 days.  In relation to the Burn Drift, the email continued:
“The other drift, to the immediate south of Derwentside House is issuing carbon dioxide at an average of 10% and bushes directly in line with the mouth of the adit can be seen to be moving with the force of the outrush.  Again, as above, at this percentage unconsciousness results after a few minutes and continued exposure thereafter could be fatal.  You will be aware that Mrs Willis has expressed concern that the gas issuing from this mine entry is causing distress to her peg dogs.  She has contacted us several times with the same accusation.”
The email concluded with an expression of the Coal Authority’s concern about the health and safety implications arising from the discovery and the fact that, after eight weeks’ prior notice to the Council, nothing had been done by the Council, nor had it accepted responsibility for the consequences, pursuant to the terms of the 1978 Conveyance.
29.	In mid-July the Coal Authority decided to test for stythe gas within the House, by installing sensors in various rooms.  These immediately revealed raised levels of CO², in particular during the night, as a result of which Mr and Mrs Willis and their family were evacuated from the House by the end of the month.  Although offered alternative accommodation, their desire to continue to look after their animals during day and night meant that they were accommodated initially in a caravan, then in two Portacabins and, shortly thereafter, in a single larger Portacabin, all on or adjacent to the Property, but far enough from the mouth of the Burn Drift to remove a risk of asphyxiation.
30.	The evacuation was designed not to place the House out of bounds to the Willises, but rather to ensure that they did not use it for sleeping, the Coal Authority’s perception being that the levels of CO² measured in the House constituted a risk only if persons were exposed to it continuously for several hours.  Accordingly, the Willises slept in the Portacabin, but used the toilet and other facilities in the House.  There was some difference in the evidence as to the extent to which they felt safe to use it for cooking and relaxation as well as for the use of baths and lavatories.   To the limited extent that it matters, I find that the predominant use of the Portacabin was for sleeping only.
31.	The Council and the Coal Authority had by the end of July reached an uneasy truce as to the responsibility for dealing with the gas escape, reflected in an exchange of correspondence between Mr Olivant and Mr Rocks-Menon of the Council’s legal department.  The Coal Authority agreed to design, commission and supervise the remedial works.  The Council agreed to reimburse the Coal Authority for its expenditure and to pay for the temporary on-site sleeping accommodation for the Willises, but subject to a continuing reservation of rights as to the ultimate liability and financial responsibility for the works.
32.	The Coal Authority’s initial perception was that the increased CO² levels at the Property, both in and outside the House, were mainly attributable to the large volumes of stythe gas emerging from the mouth of the Burn Drift.  Nonetheless, by the end of July, it is evident from emails between the Coal Authority and the Council that the Coal Authority had begun to suspect that the water discharge pipe under the Burn Drift might be an additional contributor of gas, in particular to the House, by means of what were suspected to be underground connections between that pipe and service runs for the House.  Nonetheless, the Coal Authority’s initial response to the problem was to create a temporary blockage inside the mouth of the Burn Drift, and to vent the gas through an opening cut in the roof of the Drift, through a temporary vent or chimney erected above it, the intention being that the gas would disperse into the atmosphere, rather than run at ground level from the mouth of the Drift and pool within the Property.  This temporary venting system was installed at the end of July, and its effect then monitored by gas sensors both inside the House and in the garden of the Property.
33.	Those measurements (some records of which survive) suggested by September 2006 that the temporary blocking and venting of the Burn Drift had not produced the expected reduction in CO² levels either in the rear garden of the Property or in the House.  Furthermore, temporary closure of the vent, sufficient to prevent gas flowing down from the chimney into the Property altogether, still left substantial levels of CO² in the Property.  The result was that the Coal Authority’s attention became increasingly focused upon the underground drain as a primary source of the gas emissions.  An internal report by the Coal Authority in September suggested that, although emission from the Drift itself was still a main contributor, the passage of gas through the underground drain was likely to be increased whenever the vent was closed.  Thus the design solution for a permanent remedy then contemplated was both to vent the Drift at a location further from the Property to avoid the risk of gas reaching the Property from the vent itself, and to isolate any underground routes by which gas might pass from the Drift to the Property and, in particular, the House.
34.	This perception led to the investigation of the underground drain by the use of mobile remote control CCTV cameras inserted into the drain through existing manholes located in the garden of the Property, and on the land to the north of it, where the overflow drain continued down to the River Derwent.  The drain was found to be in generally poor condition, with obstructions both north and south of the House sufficient to prevent any CCTV examination of the drainage and sump (if any) beneath the House itself, albeit that a dye test showed a slow transmission of water between the two manholes either side of the House.
35.	This led to a decision to create a water trap within the manhole in the garden of the Property (“Manhole A”) sufficient to prevent any passage of gas from there towards the House, while allowing water to continue to pass along the drain under the House and down to the river.  Continuing measurements in the House and garden showed that this step had a decisive effect in reducing CO² levels both in the House and the garden.  Further measurement during November and early December led to the Coal Authority assuring the Willises that it was safe for them to re-occupy the House, even for sleeping purposes, which they did at about Christmas 2006.  There is no evidence that stythe gas emanating from the Council’s land has constituted a nuisance at the Property thereafter, such residual levels as can still be measured there being attributable by Professor Younger (whose evidence I accept on this point) to the fact that the House is itself built on colliery waste, which probably contains a sufficient element of CO² carboniferous material.  But it is not suggested that those residual levels represent a threat to the health or safety of humans, animals or birds on the property, or that they detract in any significant way from its use and enjoyment.
36.	Following the installation of the water trap at Manhole A, the Coal Authority set about planning a permanent solution to the problem.  An internal report in October 2006 shows that the Authority continued to believe that it was necessary to vent the Burn Drift rather than just to seal it, due to the risk that sealing it could cause uncontrolled gas emissions elsewhere.  The perception continued to be that the presence of stythe gas on the Property had been caused both by escape from the mouth of the Drift and through the underground drain.  Accordingly, the design for a permanent solution included the gas tight blocking of the mouth of the Drift, the piping of gas to a new permanent vent structure constructed further from the Property to the west, and the re-routing of the underground drain around the east side of the Property to new junction with the remainder of the drain north of the Property, to an outfall at the river.
37.	These permanent works were constructed during the first half of 2007.  They involved substantial excavations, trenching and engineering works on three sides of the Property and further substantial interference with its peaceful enjoyment by the Willises, although Mr Willis fairly acknowledged in cross-examination that, having regard to the extent of the works, he could not say that the level of disturbance to his family was greater than that which was reasonably necessitated by their execution.  In the meantime the Church Drift was simply sealed off to prevent further gas emission there, it being concluded that venting was unnecessary.
38.	A detailed Health and Safety File prepared by the Coal Authority for the Council after the remedial works had been monitored for 18 months concluded that it had successfully dealt with the gas emissions from both drifts, and would continue to do so provided that the works were monitored and maintained in accordance with a detailed specification.  The monitoring and maintenance programme was designed to deal with the following specified risks:
a)	Blockage of the new vent (to the west of the Property) and the duct leading to it from the sealed mouth of the Burn Drift, for example by falling leaves.
b)	Sedimentation or blockage of a steel weir in the base of a new manhole (“Manhole E”) constructed on the site of the now sealed mouth of the Burn Drift, where gas and water were separated and re-routed.
c)	Deterioration of the old pipe, north of the Property, on its route to the river, with a view to eventual replacement should it become blocked.
d)	Deterioration of the drainage pipe leading from the swallow to Manhole E, the blockage of which would cause water to be diverted along the last part of the Burn Drift to a newly constructed overflow pipe at Manhole E.
39.	The scheme for addressing these risks was based mainly upon six monthly inspections, including in particular an inspection with the assistance of breathing apparatus within Manhole E designed to check both that the steel weir remained unblocked and that water was continuing to flow through the pipe beneath the Burn Drift, rather than the steel overflow pipe designed to provide short-term protection against its blockage.  The overflow pipe was, in particular, not regarded as a permanent solution to that risk of blockage.  Rather, the Health and Safety File prescribed a replacement of the drainage pipe between the swallow and Manhole E as an urgent requirement should the passage of water down the overflow pipe reveal it to have become blocked.
40.	The Coal Authority’s design, and in particular the overflow pipe to which I have just referred, was based upon an assumption that a blockage of the underground drainage pipe between the swallow and Manhole E would cause no greater problem than a temporary re-routing of the water flow, leaving gas still being safely vented through the new chimney installed to the west of the Property.  Further investigation by Mr Jackson led to his conclusion (with which Professor Younger agreed) that, before rising water in the Drift caused by a blockage of that underground pipe reached the new steel overflow pipe, it would already have reached the roof of the Drift at its lowest point above the swallow, thereby blocking the flow of gas as well.
41.	Monitoring of the remedial works by the Coal Authority ceased at or about the end of 2008 without any further escapes of stythe gas on to the Property.  By that time the Council had paid for the works carried out by the Coal Authority, albeit without admission of liability to do so.  The Council has not thereafter sought to challenge the Coal Authority’s assertion that it was liable for the cost, nor have any proceedings between the Council and the Coal Authority been instituted in relation to that question.
42.	Whether because of that impasse or because of the absorption of the Council into the Durham County Council in 2009, nothing was done after 2008 to monitor or carry out any routine or other maintenance in relation to the remedial works until 2011, and then only in response to a question raised by Professor Younger when preparing his expert evidence for these proceedings namely, whether the works were being monitored or maintained.  As a result of that question, the Council instructed its retained waste management contractors, Premier Waste Management Limited (“Premier”) to carry out monitoring.  No reference was made to the Health and Safety File or the programme for monitoring and maintenance set out therein.  In the event, all that was done was to conduct a brief annual gas test at the new vent to the west of the Burn Drift, and to check that water was still flowing from the outfall of the re-routed drainage system at the bank of the river.
43.	These two checks were carried out in February 2012 and 2013.  On both occasions water was observed to be flowing from the drain into the river.  In 2012 stythe gas was detected at the vent, but not in 2013.  On neither occasion was there any inspection of Manhole E.  
44.	Finally, despite requests by the Willises, no certificate of satisfactory completion of the remedial works was ever obtained by the Council, either from the Coal Authority or its contractors.  The combined effect of the absence of any such certificate and the on-going dispute between the parties’ experts as to the effectiveness of the remedial works means that, as both valuers agree, the Property is both un-mortgageable and un-sellable, and likely to remain so until those difficulties are addressed, even though there has been no continuing escape of stythe gas on to the Property, or within the House, since the completion of the works.
The Law
Rylands v Fletcher
45.	The doctrine established by the House of Lords in Rylands v Fletcher (1866) LR 1 Ex 265 (1886); LR 3 HL 330 imposes a form of strict liability upon a person who for his own purposes brings on to his land, collects and keeps there anything likely to do mischief if it escapes.  But it has long been held that mining activity is a natural user of land to which the doctrine does not apply: see Clark Lindsell on Tortes (20th Ed.) at paragraph 20-52, and Wilson v Wardell (1876) 2 App Cas 95. Nor is stythe gas something brought on to the land in the relevant sense.  It is something released by the natural reaction of oxygen with carboniferous strata.
46.	The result is that, as Mr Smith for the Council submitted, the doctrine of Rylands v Fletcher has no application in the present case.
Nuisance
47.	The essence of nuisance is a condition or activity which unduly interferes with the use or enjoyment of land.  Liability for private nuisance arises from conduct (which may be acts or omissions) which gives rise to an interference with, disturbance of or annoyance to a person in the exercise or enjoyment of his ownership or occupation of land, or of some right used or enjoyed in connection with it: see generally Clark & Lindsell (op. cit.) at paragraph 20-01.
48.	Where the defendant sued in nuisance has not caused it, but rather permitted it to continue, then proof of negligence on the defendant’s part is essential.  In Sedleigh-Denfield v O’Callaghan [1940] AC 880 at 905 Lord Wright said:
“If the defendant did not create the nuisance he must, if he is to be held responsible, have continued it, which I think means simply that he neglected to remedy it when he became or should have become aware of it.”
49.	In Leakey v National Trust [1980] 1 QB 485 at 524, Megaw LJ provided this useful general analysis of the scope of the landowner’s duty in such circumstances:
“The duty is a duty to do that which is reasonable in all the circumstances, and no more than what, if anything, is reasonable, to prevent or minimise the known risk of damage or injury to one’s neighbour or to his property.  The considerations with which the law is familiar are all to be taken into account in deciding whether there has been a breach of duty, and, if so, what that breach is, and whether it is causative of the damage in respect of which the claim is made.  Thus, there will fall to be considered the extent of the risk; what, so far as reasonably can be foreseen, are the chances that anything untoward will happen or that any damage will be caused?  What is to be foreseen as to the possible extent of the damage if the risk becomes a reality?  Is it practicable to prevent, or to minimise, the happening of any damage?  If it is practicable, how simple or how difficult are the measures which could be taken, how much and how lengthy work do they involve, and what is the probable cost of such works?  Was there sufficient time for preventive action to have been taken, by persons acting reasonably in relation to the known risk, between the time when it became known to, or should have been realised by, the defendant, and the time when the damage occurred?  Factors such as these, so far as they apply in a particular case, fall to be weighed in deciding whether the defendant’s duty of care requires, or required, him to do anything, and, if so, what?”
50.	Generally speaking, nuisance consists of the interference with some proprietary right in or in relation to land, so that a mere licensee will generally have no cause of action: see Clark & Lindsell (op. cit.) at paragraph 20-63.  The rather uncertain nature of the Willises’ rights in relation to the smallholding adjoining the Property raised, at least in theory, the question whether they could sue for nuisance in respect of animals gassed while stabled in the barns which they had built on the smallholding.  Mr Smith took no point about this.  In my judgment he was wise not to do so.  Whatever the precise nature of the arrangements between the Willises and the Council in relation to the smallholding, it seems to me likely that they enjoyed exclusive occupation at least of the barns so as (at least) to fall within what has become to known as “the peculiar status of a ‘tolerated trespasser’” originally coined by Sir Christopher Slade in Pemberton v Southwark LBC [2000] 1 WLR 1672.  Plainly the Willises’ title to the Property itself was a sufficient basis for a claim in nuisance.
Analysis
51.	It is not suggested that the Council caused the escape of stythe gas on to the Property.  Its liability if any arises only from a failure to take reasonable steps to abate it, once it knew or ought to have known about it.  Mr Knox for the Willises submitted that the Council should have known of the risk of such an escape from the moment of its acquisition of the land surrounding the Property, having regard to the express provisions in the 1978 Conveyance requiring the Council to fill in all relevant drifts and shafts, including the mouth of the Burn Drift shown on the plan annexed to the Conveyance.  I reject that submission for the reasons which follow.
52.	By 1978 the Property had been used as a private residence for nearly 20 years, with no complaint from its occupants that anything coming from the Burn Drift interfered with the enjoyment of the Property, still less with the safety of its occupants, or their animals.  I accept Mr Smith’s submission that the probable purpose for the extraction from the Council of a promise to fill in the drifts and shafts was more connected with the need to exclude trespassers from putting themselves at risk by entering them, than to seal them for the purpose of preventing the emission of gas.
53.	Although there had been isolated incidents of damage, including personal injuries, caused by gas escapes from disused mines, it had by no means led to a perception, even by the Coal Board, that all disused shafts and drifts needed automatically to be sealed against gas escape, still less a perception that the emission of stythe gas from open shafts and drifts would not ordinarily be satisfactorily dissipated in the atmosphere.
54.	In any event, the identification of a date earlier than April 2006 from which the Council should be regarded as having come under a duty to abate the nuisance constituted by the gas escape from the Burn Drift would only be material to the Council’s present liability if either (a) the taking of reasonable steps to abate it would have been completed before the Willises acquired the Property, so as to cause them no dislocation and inconvenience or (b) if it could be shown that some of their animals had died through asphyxiation before June 2006.  As to (a) the Council acquired the surrounding land less than six months before the Willises acquired the Property.  It contained a number of shafts and drifts such that, even if the Council had begun considering filling them in, in accordance with its covenant, soon after acquisition, it could hardly be said to have unreasonably failed to deal with the Burn Drift five months later.
55.	The result is that in my judgment the Council came under an obligation to remedy the gas escape from the burn Drift only in April 2006.  
56.	Mr Smith submitted that, even then, the Council never came under any obligation to remedy that part of the gas escape which flowed along the underground drainage pipe beneath the Burn Drift and which, were I to accept Professor Younger’s evidence in full, was the sole contributor to the presence of stythe gas within the House itself.  That submission raised two distinct questions of analysis.  The first was whether any liability in private nuisance could arise in respect of gas passing merely through, rather than originating in the Council’s surrounding land, it having probably passed into the drain at the water collection point in the swallow lying south of the Council’s land.
57.	I acknowledge that there is a superficial attraction in the submission that there is a large difference between nuisance constituted by the emission of gas to the surface from an open drift on the defendant’s land and the emission of gas from an underground drainage system which collects the gas outside the defendant’s land, emits it on the claimants’ land and merely passes through the defendant’s land on the way.  Certainly, a discovery of that drainage route as a source of relevant gas emissions would be likely to be less easy than the route constituted by the mouth of the Drift.  Indeed the drainage route was only suspected as a contributor to the Willis’s problems some time after the escapes from the mouth of the Burn Drift had been detected.
58.	Nonetheless, it seems to me that, in principle, the submission that the drainage route for the gas emission created no responsibility on the part of the Council, once discovered, is illusory.  The starting point is that none of the stythe gas afflicting the Property was generated on the Council’s adjoining land.  All of it passed across it from mine workings on land to the south.  Even if I had accepted that all the gas emitted into the House came from the drain,  Mr Smith did not suggest that the emissions from the mouth of the Burn Drift were not a significant contributor to the gas nuisance on the Property generally, not least because of its propensity to pool close to the ground in still conditions, particularly at night.
59.	Leaving aside increased difficulties in detecting it, it seems to me that there is nothing special in the emission of gas through an underground pipe on to a neighbour’s land which sets it apart from the emission of gas at ground level from an opening inside the defendant’s own land.  I leave on one side in that context the supply of mains gas as a service, to which very different considerations apply.  In my judgment both the mouth of the Burn Drift and the underground drain were routes by which a potentially harmful gas was until 2006 escaping from the Council’s land on to the Property.  Once discovered, both of them gave rise to an abatement duty on the part of the Council.
60.	The second question of analysis raised by this submission is whether in fact the whole of the stythe gas found to affect the House (rather than the Property generally) came through the drain, rather than from the mouth of the Burn Drift.  Professor Younger advanced an apparently persuasive opinion that it did, relying in particular upon measurements tending to show that the decisive cure of the raised gas levels in the House was the installation of a water trap in the drain at Manhole A.  He pointed out that when the works to the mouth of the Burn Drift were completed they led to no corresponding fall in the gas levels in the House, but rather to a very slight increase, albeit below levels giving rise to a nuisance.
61.	That opinion would have been compelling were it not for the fact that the measurements upon which Professor Younger relied were all taken after the installation of the temporary blocking and venting of the Burn Drift at the end of July 2006.  It seems to me probable that even this temporary process may have alleviated a prior escape of gas from the mouth of the Drift all the way into the House, and that the stopping and venting of the Drift in July 2006 may itself have increased the rate at which gas thereafter passed through the drain.  That appears to have been the view of the Coal Authority from its regular reports on the remedial works.  The result is that, even if Mr Smith’s submission (that no liability could attach to gas passing within the Council’s land through the drain) were correct, it is not demonstrated that the drain was the sole source of the nuisance, or even the sole source of gas within the House.
62.	The next question is whether any delay on the part of the Council in dealing with the nuisance constituted by the gas escape once becoming aware of it in April 2006 caused any measurable loss to the Willises beyond that which they suffered in any event by the disruption to their lives caused by evacuation, and the carrying on of substantial engineering works around them, during the year from August 2006 to July 2007.  The only candidates for identifiable loss during that period of potential delay were the boxer pups, born in May 2006, most of which then died, one by one, during the weeks following, and a litter of piglets, all of which died together with their sow during a single night on a date which the Willises were unable to identify.
63.	In my judgment there was a culpable delay between April and the end of July 2006 during which a stand-off between the Council and the Coal Authority as to which was responsible for dealing with the gas escape did cause a delayed reaction to the very real danger to the Willises and their animals which it constituted.  But I am not persuaded that either the puppies or the sow’s and piglets’ deaths can properly be treated as having been caused by that delay.  The puppies certainly qualify in terms of timing, but I am not persuaded that their deaths, which occurred on separate occasions rather than together, probably arose through asphyxiation.  By contrast, the simultaneous death of a whole litter of piglets and their sow for reasons which cannot be attributed to any specific cause other than asphyxiation appear to be a better candidate for attributing to the stythe gas escape.  The sow and her litter were kept in the barn nearest to the mouth of the Burn Drift, inside which a dangerous build-up of stythe gas may well have occurred.  The difficulty is that the evidence does not, as a matter of probability, identify those deaths as having occurred during the relevant period.  There is a log entry relating to the carrying out of the remedial work which refers to a pregnant pig having recently died before a site investigation took place on 9 November 2006.  That entry by no means locates the relevant deaths as having occurred between the end of April and July 2006.  They could as well have occurred before the end of April or after the end of July.  There is no suggestion that the temporary stopping and venting of the Drift at the end of July was an inappropriate engineering solution to the immediate dangers arising from gas escape from the mouth of the Drift, and it is likely that potentially dangerous emissions had been occurring for many years previously.
64.	I have already recorded the sensible acknowledgment by Mr Willis that the undoubted inconvenience, distress and dislocation caused by their evacuation, and by the carrying on of the remedial works around them, were no more than to be expected from the nature of the works themselves.  The Willises and their sons might have been accommodated more comfortably off-site than they were in a caravan followed by Portacabins, but it was their choice to remain on the Property while the works were being carried out, mainly to enable them to continue to caring for their livestock.  The only candidate for unreasonable intrusion into their lives constituted by the way in which the works were carried out appears to me to have been the Council’s decision not to install some form of toilet facilities within the Portacabin provided.  The result was that Mr Willis’s son was put to considerable inconvenience when, while on night shift and sleeping in the Portacabin during the day, he had to dress so as to be able to relieve himself by using the toilet in the House.  I am unable to put a figure for damages on such inconvenience, not least because of the substantial increase in the cost of the temporary accommodation provided to the Willises which would have been necessitated by the installation of toilet facilities.  As is pointed out by Megaw LJ in Leakey v National Trust, in the passage cited, cost benefit considerations are relevant to the identification of reasonable steps in the abatement of a nuisance, and I am not satisfied that the cost benefit analysis of the provision or otherwise of separate toilet facilities comes down in the claimants’ favour.
65.	A significant element of alleged loss is the fee liability which the Willises incurred to Mr Jackson, when instructing him to advise them about their predicament, before his retainer as an expert for the purpose of these proceedings.  The Council said that his retainer was quite unnecessary since the Coal Authority were designing and supervising the remedial works.  Mr Knox for the Willises submitted that his retainer was necessitated by the Council’s refusal to disclose, or allow to be disclosed, the reports and analyses being undertaken during the design and execution of the remedial works.
66.	The evidence clearly shows that Mr Cansino felt constrained to withhold materials of that kind from the Willises on advice from the Council’s legal department, apparently due to a perception that information relevant to the potential liability to the Council both to the Willises and to the Coal Authority should be kept confidential.  
67.	In my judgment the Council is liable to reimburse the Willises for that expenditure.  My reasons follow.  First, the touchstone for liability is the identification of the reasonable steps required of a landowner to abate a nuisance caused to its neighbour.  In circumstances where the nuisance in question consists of the escape of potentially asphyxiating gas from disused mine workings I consider that reasonable steps do include the provision (on request) of information to the adversely affected property owner about the causes of the escape, the levels of gas being emitted, and the design of the remedial works with which the emissions are planned to be abated.
68.	A conclusion that the Council ought to have made that information freely available to the Willises flowed naturally from Mr Knox’s percipient cross-examination of Mr Cansino on the point.  He asked Mr Cansino whether he thought the withholding of that information was fair, to which he received the stonewalling reply that Mr Cansino did not consider himself as an expert on fairness.  He was then asked whether he would have thought it was fair if he, rather than the Willises, had been the owner of the Property.  To this Mr Cansino quickly responded in the negative.
69.	In my judgment, reasonable steps to abate a nuisance of this potentially dangerous and frightening type did require the Willises to be kept informed of the Council’s developing understanding of the cause of the problem, together with the analysis and design of the remedial works being carried out by the Coal Authority upon the Council’s behalf.  They were not provided with that information, and the expenditure of money on the obtaining of advice about those matters from Mr Jackson was, in my view, a reasonable mitigation of their loss, for which they should be reimbursed. 
70.	The final question of analysis is whether the continuing (and agreed) state of affairs that the Property is un-mortgageable and un-marketable can be attributed to any failure by the Council to take reasonable steps to abate the nuisance constituted by the gas escape.  I have concluded that, as a matter of fact, the remedial works have succeeded in preventing any significant escape of stythe gas from the Council’s land onto the Property since they were completed in mid 2007.  This is because, although not monitored or maintained since the end of 2008 in accordance with Health and Safety File, the remedial works have achieved that for which they were designed, namely the re-routing of gas in the Burn Drift by venting it to the west and the re-routing of the drain to the east.
71.	There was an energetic debate between Mr Jackson and Professor Younger as to whether a failure to monitor and maintain the remedial works in accordance with the Health and Safety File hereafter could cause a recurrence of gas escape onto the Property.  It will be apparent from my description of the monitoring and maintenance recommendations in the Health and Safety File that the main on-going risks to the proper functioning of the remedial works consist of blockage to the vent, blockage of the drain at Manhole E and failure of the underground pipe between the swallow and Manhole E.  Each of those could produce a build-up of gas in the Burn Drift.  A blockage of the vent would obviously do so, not least because there is now a water trap at Manhole E which prevents gas passing down the re-routed drain to the east of the Property.  A water blockage, either in the drain between the swallow and Manhole E, or at Manhole E, could produce a build-up of water in the Drift, potentially sufficient to reach its roof and block the passage of gas at the swallow.
72.	Mr Jackson’s opinion was that, in any of those circumstances, there was a continuing risk of gas escape horizontally along the strata from the Council’s land to the Property, and in particular along those parts of the strata which had been disturbed by the construction of the underground drain in the first place.  Professor Younger’s opinion was that, in any of those circumstances, the Property would be at no greater risk of gas invasion than any of the large number of residential properties in the neighbourhood of the coal workings, since gas trapped in the mine workings currently ventilated by the Burn Drift would simply accumulate until it escaped in some unpredictable place elsewhere.  In particular Professor Younger’s opinion was that the strata in the vicinity of the Property, whether in its original condition or after man-made disturbance, was very unlikely to admit the horizontal passage of gas at low pressure.  His conclusion was that, whether or not monitored or maintained, the remedial works had provided a permanent solution to the Willises’ problems, and that it was merely unjustified alarmism on Mr Jackson’s part that stood in the way of certification of the permanent abatement of the nuisance, which he said he would be happy to provide himself.
73.	I accept Professor Younger’s evidence that, from a scientific perspective, the remedial works probably will be sufficient to dispose of any significant risk of gas escape on to the Property, even if not monitored or maintained in accordance with the Coal Authority’s recommendations.  I found Professor Younger’s evidence about the relatively impermeable nature of the strata to be compelling, in an area where his expertise was plainly greater than that of Mr Jackson, who came very near to admitting Professor Younger’s thesis that the Property was at no greater risk than other neighbouring properties, during Mr Smith’s careful cross-examination.
74.	But the fact remains that the Property is, at present, un-sellable and un-mortgageable because of the combined effect of the absence of a certificate of the satisfactory completion of the remedial works, and the existence of a dispute about their adequacy, if not satisfactorily monitored and maintained in accordance with the recommendations of the Coal Authority, which designed them.  The parties’ valuers did not attend to give evidence (because of their substantial agreement) and it was not possible to ask either of them whether a determination by the Court of the issue on which the experts disagreed would be sufficient to resolve the blight upon the value of the Property.
75.	It is of course not the law that the landowner is the guarantor of the capital value of his neighbour’s land, free from the consequences of a nuisance which is not caused by the landowner.  His responsibility is only to take reasonable steps to abate the nuisance once discovered.  Mr Smith said that, on the expert evidence, I should conclude that the nuisance has been abated, so that the Council has taken reasonable steps, and had done so by the end of 2007, even if nothing was done thereafter to provide a certificate to the Willises, or to monitor or maintain the remedial works.
76.	Again, I consider that the answer lies in the application of the principle requiring the taking of reasonable steps.  Dealing first with the certificate, the evidence shows that where engineering works of this kind are carried out, it is generally possible to obtain a certificate of their satisfactory completion, and that the existence of such a certificate goes a long way to resolve the difficulties in selling or mortgaging the land affected by the nuisance, once abated.  In the present case the Willises asked the Council for such a certificate, but there is no evidence to show that the Council took any steps to seek or obtain one from the Coal Authority or its contractors.
77.	It is in my judgment reasonable to suppose that such a certificate would have been forthcoming from the Coal Authority (which was, from the written evidence, clearly satisfied with the design and quality of the remedial works), but only upon the basis that its recommendations as to monitoring and maintenance thereafter were carried out.  It was from start to finish the Coal Authority’s opinion that the gas emission problem could not satisfactorily be dealt with merely by blocking the Burn Drift, because of the risk of unpredictable emissions elsewhere, so that the maintenance of the system of venting for the indefinite future was an essential aspect of the remedial scheme.  The monitoring and maintenance programme was specifically designed to ensure that both gas and water continued to be safely vented and drained from the Drift.
78.	I consider that a response to the nuisance constituted by gas emissions onto the Property in the form of commissioning and paying for a remedial scheme, but without either obtaining a certificate of its satisfactory completion, or committing to its monitoring and maintenance in accordance with the recommendations of its designer, falls short of the taking of reasonable steps to abate the nuisance.
79.	It struck me nonetheless both at the beginning and end of the trial that it was curious indeed that the Willises did not seek any injunctive relief in this respect or that, in the light of the unanimous opinion of the valuers that the Property is un-sellable, the Council did not, until a very late state, offer anything by way of an undertaking to monitor and maintain the remedial works in accordance with the Coal Authority’s recommendations, in the face of a substantial monetary claim for damage to the value of the Property.
80.	In his closing submissions Mr Smith did, with some encouragement from the Court, begin to put this right, and in written submissions following the hearing proposed a form of undertaking designed to address this aspect of the Willises’ claim.
81.	I regard it very unsatisfactory for the Court to have to address this aspect of the matter by granting or refusing an award in damages reflected in a £200,000 diminution in value, for as long as some much cheaper remedy in terms of certification, monitoring and maintenance of the works appears to represent a fairer, cheaper and more satisfactory solution.
82.	I propose therefore to do no more at this stage than to record that, pending the provision of a certificate of satisfactory completion of the works and the giving of an appropriate undertaking as to their monitoring and maintenance, reasonable steps have not yet been completed by the Council to abate the nuisance discovered in April 2006.  It has already been agreed that this trial should be limited to the identification of relevant heads of loss rather than their quantification.  I shall therefore, in addition, adjourn for further argument the question whether, in the light of the undertaking now offered by the defendants, any further remedy in respect of the abatement of the nuisance is required.
83.	The result is therefore that the quantification of loss occasioned by the Willises in having to instruct Mr Jackson is to be quantified by inquiry, and the further steps necessary to complete the abatement of the nuisance by certification and undertakings as to monitoring and maintenance be the subject of inquiry as well.  This will have the advantage that those additional matters can be dealt with by a District Judge, without having to await my return to Newcastle, or require the parties’ attendance in London.