Professional Negligence Contract Loss Expert Witness

Professional negligence claims against accountants, solicitors, surveyors, and other advisers require expert evidence on both liability and quantum. A contract loss expert witness in this context constructs a but-for counterfactual, establishing what the claimant's financial position would have been had the professional performed their retainer competently, and compares it to the actual outcome. This analysis underpins damages in failed transactions, negligent valuations, defective tax advice, and litigation strategy errors where the claimant alleges they would have achieved a better financial result but for the professional's breach of duty.

The SAAMCo principle (South Australia Asset Management Corp v York Montague Ltd [1997] AC 191) fundamentally limits the scope of recoverable loss in professional negligence cases. Damages are confined to losses within the scope of the professional's duty, distinguishing between advisers who provide information (where liability is limited to the additional loss caused by the information being wrong) and those who provide advice on a specific transaction (where a broader range of losses may be recoverable). Expert witnesses must address SAAMCo at the outset of their analysis, identifying which categories of loss fall within and outside the scope of the retainer.

Where the claimant's loss depends on the hypothetical actions of a third party, whether a court would have ruled in their favour, whether a buyer would have completed, or whether planning permission would have been granted, the loss of chance methodology applies. Following Allied Maples Group Ltd v Simmons & Simmons [1995] 1 WLR 1602, the expert quantifies the lost opportunity as a percentage probability multiplied by the full value of the opportunity. Causation between the negligence and the loss must be established on the balance of probabilities for past events, with appropriate discounting for contingent future outcomes. Expert reports address each head of loss separately with transparent assumptions capable of withstanding cross-examination.

Frequently Asked Questions