Loss of a chance: when the claimant only had to show a real prospect

Reviewed by Matthew Bartlett, Director · Last reviewed 2026-07-01

Where loss-of-a-chance sits in the causation picture

Most professional negligence claims turn on causation, and most causation arguments are resolved on the ordinary balance-of-probabilities test — see the companion entry on but-for causation in PI claims. The loss-of-a-chance doctrine is the recognised exception. It applies where the claimant's loss depends not on what the claimant would have done, but on the hypothetical actions of an independent third party — another solicitor, a counterparty, a court, a product provider, a tax tribunal.

The doctrine matters because so much professional work is a hinge between the client and a third-party decision-maker. A solicitor advises on a settlement offer that another party might or might not have improved. An IFA fails to arrange cover with a provider who might or might not have accepted the risk. An accountant misses a filing window that a tribunal might or might not have extended. In each case the professional's breach does not directly cause the loss; it removes the client's opportunity to secure a better outcome from someone else.

Allied Maples: the two-branch approach

The modern framework starts with Allied Maples Group Ltd v Simmons & Simmons [1995] 1 WLR 1602. Stuart-Smith LJ separated two questions. First, what would the claimant himself have done had the professional acted competently? That is decided on the balance of probabilities — if the claimant clears 51 per cent he recovers in full for that step. Second, what would an independent third party have done? That is not decided on balance of probabilities. Provided the claimant shows a "real and substantial" (not speculative) chance that the third party would have acted in the claimant's favour, the court values the chance and discounts damages by the percentage assessed.

Perry v Raleys: the Supreme Court reformulation

Perry v Raleys Solicitors [2019] UKSC 5 tightened the framework for solicitors' negligence. Lord Briggs confirmed the two stages but made clear how each is discharged. The claimant must first prove, on the balance of probabilities, that he would have taken the step the negligent solicitor deprived him of — pursuing the claim, accepting the offer, signing the deed, applying to the scheme. Only if that hurdle is cleared does the court turn to the hypothetical third-party outcome and value the chance as a percentage.

Lord Briggs was firm that stage one is a real hurdle, not a formality. A claimant who cannot honestly say he would have acted differently gets nothing. That has narrowed some of the more optimistic pleadings the Court of Appeal had allowed through in cases such as Mount v Barker Austin [1998] PNLR 493 and Dixon v Clement Jones Solicitors [2004] EWCA Civ 1005, though the two-stage architecture in those decisions remains good law for valuing the chance itself.

Worked example (hypothetical — for illustration only)

A solicitor misses the three-year limitation deadline on a client's personal injury claim. The client sues the firm in professional negligence. Applying Perry v Raleys:

• Stage one — would the client, on the balance of probabilities, actually have pursued the underlying personal injury claim to trial or settlement had the firm acted competently? If the evidence shows she was ambivalent or had already indicated she wanted to walk away, she fails at stage one and recovers nothing.
• Stage two — if she clears stage one, the court values the lost claim. Say the underlying claim was worth £120,000 if won in full, and the court assesses a 60 per cent chance she would have succeeded against the original tortfeasor. Damages are £120,000 x 60 per cent = £72,000, subject to any further discount.

Practical impact on PI claims across the professions

The doctrine sits behind a large share of PI notifications Apex sees from solicitors, IFAs and accountants. For solicitors, most missed-limitation and lost-litigation claims are analysed this way — see the wider treatment in the solicitors' PI insurance guide. For IFAs, cases where the client says a different product would have been available from a different provider fall into the same framework — the IFA PI insurance guide discusses the interaction with FOS awards. For accountants, missed appeal deadlines against HMRC assessments turn on the tribunal's hypothetical response and are addressed in the accountants' PI insurance guide.

The doctrine also interacts with the scope-of-duty question. Even where a loss of chance can be shown, damages are recoverable only if the lost opportunity fell within the professional's duty — the point developed in the entry on the SAAMCO principle and scope of duty.

Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority. Firm reference number 724952. This entry is general information, not advice on any particular policy.

Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority. Firm reference number 724952.