Solicitors must align pleadings, expert instructions, and disclosure with the correct legal framework before significant costs are incurred on quantum analysis that the court cannot ultimately award.
But-For Counterfactual in Professional Negligence
The starting point for quantification is the but-for counterfactual: what would the claimant's financial position have been had the professional performed their retainer competently? This requires careful reconstruction of the transaction, advice, or valuation that was negligently performed.
For accountant negligence in a transaction, the expert compares the actual outcome with the outcome that would have occurred with competent advice, including whether the transaction would have proceeded at all. For valuer negligence, the expert compares the actual property or asset value with the true value that a competent valuation would have disclosed.
The counterfactual must be realistic and supported by contemporaneous evidence. Where the claimant would not have proceeded with the transaction even with competent advice, the loss may be limited or nil. The expert should address this explicitly rather than assuming the transaction would have succeeded.
The SAAMCo Principle and Scope of Duty
South Australia Asset Management Corp v York Montague Ltd [1997] AC 191 (SAAMCo) limits damages to losses within the scope of the professional's duty. Where the professional provides information for a specific purpose, liability is limited to the loss flowing from the information being wrong, not all losses flowing from the transaction.
The distinction between 'advice' and 'information' cases is critical. In advice cases, the professional is responsible for the claimant's decision to enter the transaction. In information cases, the professional is responsible only for the consequences of the specific information being inaccurate.
Expert witnesses must be instructed on which category applies and structure their analysis accordingly. Quantifying the full transaction loss when the duty was limited to a valuation figure is a common error that renders expert evidence inadmissible or unpersuasive. Solicitors should obtain counsel's advice on scope of duty before finalising expert instructions.
Loss of Chance Quantification
Where the claimant's loss depends on the actions of a third party, whether a court would have ruled in their favour, whether a transaction would have completed, whether planning permission would have been granted, the claim is for loss of a chance. The expert quantifies the value of the chance lost, not the full outcome value.
In Allied Maples Group Ltd v Simmons & Simmons [1995] 1 WLR 1602, the Court of Appeal held that where the defendant's negligence deprives the claimant of the chance to negotiate a better settlement, damages reflect the lost opportunity. The expert assigns a percentage probability to the chance and multiplies by the full value of the benefit that would have been obtained.
The percentage must be supported by evidence, comparable cases, legal opinion on prospects, or market data, not arbitrary expert impression. Courts scrutinise loss of chance calculations closely. The expert should present a range where appropriate and explain the basis for the selected probability.
Allied Maples and Solicitor Negligence Claims
Solicitor negligence claims frequently involve loss of chance, the chance to settle, the chance to succeed at trial, or the chance to complete a transaction. The expert works with the legal team to assess prospects of success at the relevant date, applying the information available at that time (not hindsight).
For litigation negligence, the expert may need to value the underlying claim that was compromised by the negligence, then apply a percentage discount for litigation risk. This requires coordination between the quantum expert and counsel advising on legal merits.
Solicitors should ensure the expert does not usurp the legal function of assessing case merits. The expert quantifies the financial value of outcomes; counsel advises on legal prospects. A joint approach produces the most defensible loss of chance calculation.
Expert Report Structure for Professional Negligence
A professional negligence quantum report should follow this structure: instructions and assumptions; background and chronology; scope of duty analysis (confirming alignment with legal advice); but-for counterfactual; actual outcome; causation analysis linking negligence to loss; loss of chance calculation (if applicable); mitigation; summary of net loss; and appendices with financial schedules.
CPR Part 35 requires the expert to state when a question falls outside their expertise. Legal conclusions on duty, breach, and scope are for the court. The expert addresses quantum on the assumptions instructed.
Early joint expert meetings in professional negligence cases should focus on: agreed chronology; scope of duty category; but-for assumptions; and the probability percentage for any loss of chance. Narrowing these issues early saves substantial trial preparation costs.
Frequently Asked Questions
What is the SAAMCo principle in simple terms?
SAAMCo limits professional negligence damages to losses within the scope of what the professional was engaged to advise on. An information provider is not liable for all transaction losses, only those caused by the specific information being wrong.
How is loss of chance different from but-for analysis?
But-for analysis assumes a definite outcome absent negligence. Loss of chance applies where the outcome depended on a third party's decision, and the expert quantifies the probability-weighted value of the lost opportunity.