Professional negligence claims often present complex challenges for the Courts, particularly when assessing damages. While some claims involve a direct, quantifiable loss, others concern a hypothetical counterfactual – a 'lost opportunity'. In these circumstances, the English Courts apply the doctrine of 'loss of a chance', a nuanced approach to causation and quantum that significantly impacts both claimants and professional indemnity insurers.
The conventional test for causation in negligence is the 'but for' test: would the claimant have suffered the loss 'but for' the defendant's breach of duty? This generally requires the claimant to prove, on a balance of probabilities, that the defendant's negligence caused their loss. However, this straightforward approach becomes problematic when the alleged loss is not a certainty but depends on a hypothetical future event or the contingent actions of a third party. The House of Lords in Hotson v East Berkshire Area Health Authority [1987] AC 750 applied the 'all or nothing' principle to a lost chance of recovery from an existing injury, but this was distinguished in subsequent professional negligence cases involving a lost commercial opportunity.
The seminal authority for loss of a chance in professional negligence is Allied Maples Group Ltd v Simmons & Simmons [1995] 1 WLR 1602. In that case, solicitors failed to advise their client on potential liabilities arising from a property transaction, thereby depriving the client of the opportunity to negotiate a warranty or indemnity. The Court of Appeal held that where the claimant's loss depends on a hypothetical future action of a third party, the claimant does not have to prove that the third party would have acted to their benefit on a balance of probabilities. Instead, the Court assesses the value of the lost chance itself.
This established a crucial two-stage test. First, the claimant must prove, on a balance of probabilities, what they themselves would have done had they received proper advice (e.g., attempted to negotiate a warranty). Second, if they establish this, the Court then assesses, as a percentage, the probability that the third party would have acted in a way that would have benefited the claimant (e.g., granted the warranty or made a concession). The damages awarded reflect this percentage of the full value of the opportunity.
It is important to note that the lost chance must be ‘real or substantial’, not merely speculative. The claimant bears the burden of adducing sufficient evidence to demonstrate that a tangible opportunity was indeed forgone. This often requires careful reconstruction of the counterfactual scenario, potentially involving expert evidence on market conditions, commercial negotiations, or even the likely stance of the hypothetical third party. Without a 'real' chance, the claim for loss of a chance will fail.
Quantifying the value of such a chance is inherently difficult and remains a question of fact for the judge. The Courts frequently acknowledge the broad-brush nature of this assessment, weighing all the available evidence to arrive at a fair percentage. This process is far from an exact science and requires careful judicial scrutiny of the counterfactual reality that the claimant asserts would have unfolded but for the professional's negligence.
For regulated professionals and their insurers, understanding the principles of loss of a chance is critical. Claimants must rigorously present their case to establish a real and substantial lost opportunity and provide a credible basis for its valuation. Conversely, defence teams must meticulously challenge not only the alleged negligence, but also the very existence of a lost chance, whether it was 'real', and crucially, the percentage valuation applied to that chance. A robust defence strategy involves scrutinising the counterfactual evidence and presenting alternative, less favourable, scenarios to the Court.