Duress and undue influence
When consent is vitiated by illegitimate pressure or the exploitation of trust and vulnerability.
Overview
Duress and undue influence stand as two conceptually distinct but functionally allied doctrines that police the voluntariness of contractual consent. Both render a contract voidable rather than void, conferring on the victim a right to rescind subject to the usual bars (affirmation, laches, third-party rights, impossibility of restitution). Their core concern is whether the claimant's apparent consent was sufficiently free to ground the law's enforcement of the bargain.
Duress is a common law doctrine that has expanded from threats of physical violence (duress to the person) to encompass economic pressure (Universe Tankships Inc of Monrovia v International Transport Workers' Federation [1983] 1 AC 366). Its modern test is whether an illegitimate threat causally induced the claimant to contract in circumstances in which he had no practical alternative. The legitimacy enquiry turns on whether the conduct threatened is itself lawful and whether the demand is legitimate.
Undue influence is an equitable jurisdiction that comes in two broad forms. Actual undue influence (Class 1) requires proof that the dominant party exerted influence over the transaction itself. Presumed undue influence (Class 2) arises where a relationship of trust and confidence exists and the transaction calls for explanation; once presumed, the onus shifts to the defendant to rebut by showing the claimant exercised independent and informed judgment. In three-party cases (especially guarantees given by surety spouses), the leading authority is Royal Bank of Scotland v Etridge (No 2) [2001] UKHL 44, [2002] 2 AC 773, which clarifies when a creditor is put on inquiry and what steps suffice to discharge that burden.
Because these doctrines grew up separately—duress at law, undue influence in equity—they retain distinct tests and vocabularies, though both share a concern with the quality and freedom of consent. In practice, claimants often plead both in the alternative, particularly in commercial disputes involving renegotiation under pressure.
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