There was no rule of law that if the only other possible causes of an event were very much less likely than one suggested means of causation, that became the probable cause; the court had to be satisfied on rational and objective grounds that the case for believing that the suggested means of causation occurred was stronger than the case for not so believing.

The Court of Appeal so held in a reserved judgment dismissing the appeal by the third defendant, National Insurance and Guarantee Corpn Ltd, from the order of Edwards-Stuart J sitting in the Technology and Construction Court dated 3 November 2011 [2011] EWHC 2847 (TCC) by which he made an award of damages for negligence against the first defendant, Michael Nulty (who had died since the commencement of proceedings), in favour of the claimant, Milton Keynes Borough Council.

A fire broke out at a recycling centre owned by the claimant while the first defendant, a self-employed electrical engineer, was working on the premises, alone apart from a security guard. He had according to his account set out for the staff canteen to have a cup of tea and a cigarette and had insisted to investigators and in his witness statement that he had not smoked anywhere other than in the designated smoking area. Nevertheless, the possibility of the fire having been started by a cigarette end carelessly discarded by someone smoking in the processing area, and that person being the first defendant, was one of three put to the judge at trial. The others were arson by an intruder, and arcing from an old electric cable (“the Boa cable”) which had, unknown to anyone at the time, been left live. The judge discounted arson, found it to be very unlikely that arcing was the cause, and concluded that the first defendant’s discarding a cigarette end, although inherently unlikely, was the most probable cause. He further held that the third defendant, the first defendant’s professional liability indemnity insurer, was liable to indemnify the first defendant under the insurance policy to the extent of 85% of his liability.

TOULSON LJ said that a case based on circumstantial evidence depended for its cogency on the combination of relevant circumstances and the likelihood or unlikelihood of coincidence. Consideration of such a case necessarily involved looking at the whole picture, including gaps in the evidence, whether the individual factors relied on were properly established, what factors might point away from the suggested explanation and what other explanation might fit the circumstances. There was an inherent risk that a systematic consideration of the possibilities could become a process of elimination leading to no more than a conclusion as to the least unlikely cause of loss. That was the fault identified by the House of Lords in Rhesa Shipping Co SA v Edmunds (The Popi M) [1985] 1 WLR 948. At the end of any such systematic analysis, the court had to stand back and ask itself the ultimate question whether it was satisfied that the suggested explanation was more likely than not to be true. The elimination of other possibilities as more implausible might well lead to that conclusion, but that would be a conclusion of fact. There was no rule of law that it had to do so. The balance of probability test meant that the court must be satisfied on rational and objective grounds that the case for believing that the suggested means of causation occurred was stronger than the case for not so believing. Having concluded that a cigarette end carelessly discarded by the first defendant was the most probable cause of the fire, the judge had posed the question whether on the authorities that finding was sufficient for him to hold that the claimant had discharged the burden of proof. The answer was yes, provided that he was satisfied on all the evidence that the case for believing that the first defendant had caused the fire was stronger than the case for not so believing. However the judge had gone further by stating as a proposition of law that if the only other possible causes were very much less likely, the discarded cigarette became in law the probable cause. In that respect, he had erred. It did not follow that his conclusion was wrong on the facts as he found them after a painstaking examination of the evidence. Rational analysis of the Boa cable theory showed it to be highly improbable. There was no comparable scientific or practical improbability about the discarded cigarette end theory. The judge’s conclusion as to liability had been properly open to him.

BEATSON and LONGMORE LJJ agreed.