Quick answer

A quantum meruit is a claim for a reasonable sum, arising where a benefit is conferred without an agreed price, for example where no price is fixed, where work is done during failed negotiations, or where work is done outside an existing contract, and it is evaluated on all the circumstances, with the amount of any quotation usually setting the upper limit

A quantum meruit is a claim for a reasonable sum, arising where a benefit is conferred without an agreed price, and it does not usually arise where an existing contract fixes the price. It can arise on an express agreement to pay a reasonable sum, where a contract fixes no price, where work is done during negotiations that never reach agreement, as in British Steel Corporation v Cleveland Bridge and Engineering Co Ltd, or where work is done outside an existing contract, as in Parkinson v Commissioners of Works. A quantum meruit can also be contractual: in ACT Construction Ltd v E Clarke and Sons (Coaches) Ltd an instruction to do work and its acceptance formed a contract carrying an implied obligation to pay a reasonable sum, assessed there as costs plus 15 per cent. The measure is not fixed. Courts take all the circumstances into account; costs may serve but must be reasonably and properly incurred and adjusted for inefficiency and defects, and the value of the work to the recipient may be preferred. Where a quotation was submitted but no contract concluded, Lachhani v Destination Canada (UK) Ltd holds that the quotation sets the upper limit of the entitlement.