Professional Negligence Damages Expert Witness
Professional negligence claims against solicitors, accountants, financial advisers, and other professionals require expert evidence on quantum as well as liability. A damages expert witness constructs a but-for counterfactual establishing what the claimant's financial position would have been had the professional performed the retainer competently, then compares it to the actual outcome. This analysis applies to failed transactions, negligent tax advice, defective litigation strategy, and valuation errors where the claimant alleges a better financial result but for the breach.
The SAAMCo principle (South Australia Asset Management Corp v York Montague Ltd [1997] AC 191) limits recoverable loss to damages within the scope of the professional's duty - distinguishing information providers from transactional advisers and capping exposure where the professional's negligence was not the sole cause of loss. Expert witnesses identify which categories of loss fall within and outside scope before quantifying the remainder, addressing attribution between negligence, market movements, and the claimant's own decisions.
Where outcomes depended on third-party conduct - judicial decisions, planning permission, or transaction completion - Allied Maples loss of chance principles require probability discounting of the full opportunity value. Reports set out each head separately with transparent assumptions, sensitivity analysis on key probabilities, and methodology capable of withstanding cross-examination in the Chancery Division and professional negligence lists.
Frequently Asked Questions
What is the SAAMCo principle in professional negligence?
The SAAMCo principle (South Australia Asset Management Corp v York Montague [1997]) limits the damages recoverable in professional negligence cases to the loss within the scope of the professional's duty. Where an adviser provides information (not advice), their liability is limited to the additional loss caused by the information being wrong - not all losses flowing from the transaction. Expert witnesses must address SAAMCo when quantifying professional negligence losses.
What is loss of chance quantification?
Where the claimant's loss depends on the actions of a third party (e.g. whether a court would have decided in their favour, or whether a transaction would have completed), the expert quantifies the loss of chance - expressing the lost opportunity as a percentage probability multiplied by the full loss. This approach is common in solicitor negligence claims (Allied Maples v Simmons & Simmons [1995]).
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