Background

Two airline pilots, Mr Gough and Mr Montague-Trenchard, alleged they suffered from aerotoxic syndrome (ATS) due to repeated exposure to toxic fumes while flying for Thomas Cook Airlines and Etihad Airways.

  • In 2013, they consulted a Scottish law firm, which negligently failed to pursue their claims.

  • By 2014, collective ATS proceedings were being prepared in England, but the pilots missed the limitation deadline.

  • Left without recourse against their employers, they sued their Scottish solicitors for breach of contract and loss of chance.

The law firm admitted breaching its duty of care but disputed causation, arguing that the pilots’ prospects of success were minimal. The pilots argued that they had excellent prospects on their underlying claims and that their loss of chance should be assessed at the top-end of the range (80%), while the law firm contended that the prospects were limited to no more than 20%.

The judgment

Lord Richardson delivered a 161-page decision, applying established principles from Allied Maples and Perry v Raley. The decision reiterated that the court must apply a two-stage test when assessing a loss of chance claim. 

  • The first stage involves a fairly conventional adversarial assessment of whether the claimants can prove on the balance of probabilities that if properly advised, they would have pursued the lost opportunity (in this case, pursuit of the airline claims).

  • The second stage is more complex because the court is required to assess the claimant's hypothetical counterfactual involving third parties who are usually not available to give evidence on what they would have done (in this case, the airlines and how they would have responded to the pilots' claims). Here the court assesses the value of the lost chance by determining the percentage probability of the chance occurring and then applies this percentage to the potential benefit that was lost. This often follows evidence and argument on a range of potential outcomes (as was the case here regarding the underlying prospects of the claims against the third-party airline(s) had they been pursued).

The court found that, with proper advice, the pilots would have joined the English ATS group litigation before limitation expired. The court assessed the pilots’ chances at 40%, rejecting both extremes. The award at 40% reflected both the real prospects of success and the inherent uncertainties of ATS litigation. As the English group proceedings head to trial in 2026, Gough provides a timely precedent on how courts balance negligence, causation, and the speculative nature of lost opportunities.

Key takeaways

  • Even where negligence is admitted, damages hinge on the viability of the lost opportunity.

  • Courts will adopt a broad-brush approach to determining the percentage to be applied to the lost chance and will, where possible, avoid conducting a “trial within a trial” when assessing hypothetical outcomes.

  • This stage is more speculative and involves a degree of estimation on how third parties would have acted. As the judge found in Gough, detailed analysis would result in significant unfairness relating to "difficulties caused by the passage of time, difficulties caused by the absence of the third-party defender; and difficulties in relation to the recovery of documents or the tracing and/or memories of witnesses".

  • Courts will weigh expert and factual evidence carefully but ultimately apply a percentage discount to reflect litigation risks.