English court issues reminder of burden of proof in product liability cases

The ruling came after experts were divided as to the cause of fire that wrote off a recently-purchased Volkswagen car. Its owner, Mr Nash, sought damages from the manufacturer after the vehicle burst into flames while parked on his driveway, claiming that it was not of satisfactory quality.

Both parties accepted that, where the court is presented with a number of competing explanations for a particular event and finds that one of them is more likely than the others, the court is not obliged to accept that explanation – and did not do so in this case. In other words, a court is not simply invited to choose the least improbable of the explanations offered to it. Proof of causation on the balance of probabilities must be demonstrated, failing which it remains open to the court to decide that the burden of proof has not been discharged and to dismiss the action.

In coming to its decision, the court approved the two-stage test – that to prove their case a claimant must convince the court that their version of events is more likely than not to have been the cause of the damage. This requires them to show that it is both:

• more likely than any competing version of events; and
• that it is not so inherently improbable that even if it is preferable to a competing version of events, it is still not enough to discharge the burden of proof.

However, it also confirmed that in an appropriate case, it is sufficient to ask “the single unitary question” and decide the case accordingly without having selected which of competing explanations is the more probable. In this case, that single unitary question was whether the court was able to find that it was more likely than not that the fire was caused by a fault, albeit unknown, in the vehicle.

While it does not create new law, the ruling is particularly relevant to cases involving disputed factual causation, particularly where there are competing explanations. Where competing explanations for causation are mooted, claimants must ensure their evidence does not just provide a more probable explanation for the damage claimed than any other but that on the balance of probabilities it can explain it.

Where experts are involved, their report should address this issue, and ensure that supporting evidence is provided. It is not sufficient simply to suggest that the explanation they put forward is the least improbable. Other possible explanations should be tested, and suitable explanations given as to why they should be dismissed.