Restitution and unjust enrichment

Restitution and unjust enrichment sit awkwardly but indispensably within a Contract paper. They are not simply a remedial appendix to breach. Nor are they a disguised form of contractual expectation. Their central question is different: has the defendant been enriched at the claimant's expense in circumstances which make it unjust for the defendant to retain the enrichment, subject to any applicable defence? Contract asks whether a promise is binding and what performance or substitute money must follow from its breach. Unjust enrichment asks whether a transfer, service, payment, release or other benefit lacks a sufficient legal basis for retention.

The connection with contract is nevertheless close. Many unjust enrichment claims arise in contractual settings: money paid under a void, voidable, frustrated, discharged or anticipated contract; benefits conferred during negotiations which never mature into a contract; services rendered under an agreement later found ineffective; overpayments made under a binding contract; or payments exacted under duress, undue influence, mistake or illegality. Cambridge essays often test whether students can keep these categories separate without sealing them off from one another. The best answers do not say merely that restitution is available where contract fails. They ask what precisely has failed: the existence of the contract, the condition of the payment, the validity of the claimant's consent, the performance for which the benefit was transferred, or the legal power of the recipient to demand the money.

The modern English law of unjust enrichment is usually organised through four questions. First, has the defendant been enriched? Secondly, was the enrichment at the claimant's expense? Thirdly, is there an unjust factor, such as mistake, duress, failure of basis, undue influence, legal compulsion or the Woolwich principle for unlawful demands by public authorities? Fourthly, is there a defence, most importantly change of position, bona fide purchase, passing on, estoppel or counter-restitution difficulties? That formula is orthodox after Banque Financiere de la Cite SA v Parc (Battersea) Ltd and subsequent authority, though its edges remain contested.

For Contract revision, three themes matter most. The first is failure of basis. Money paid for a contractual purpose may be recoverable where the basis on which it was paid fails. The historical language was total failure of consideration, but modern usage prefers failure of basis because the inquiry is not the doctrine of consideration in contract. The second is the relationship between restitutionary claims and contractual risk allocation. If a valid contract allocates the risk of non-performance or non-occurrence, unjust enrichment must not rewrite the bargain. The third is valuation. Restitution is generally measured by the value of the enrichment received, not the claimant's loss or the promised contract price, but contractual contexts complicate the assessment, especially where services were requested, partly performed, subjectively devalued, or rendered under an unenforceable agreement.

In Tripos terms, this is a topic where doctrinal discipline is rewarded. A strong answer states the unjust enrichment structure, identifies the contractual setting, explains whether the contract supplies or excludes a basis, then applies the relevant unjust factor and defences. A weak answer treats restitution as a discretionary fairness jurisdiction. It is not. The vocabulary of justice is mediated through rules, categories and policies concerning autonomy, risk, security of receipt and the integrity of bargains.

English restitutionary liability emerged from forms of action long before unjust enrichment acquired its modern analytical form. The common counts, especially indebitatus assumpsit for money had and received, permitted recovery where the defendant had received money which in justice ought to be returned. Lord Mansfield's judgments in the eighteenth century gave this jurisdiction its famous equitable language, but the liability was common law. The older law did not possess a single coherent taxonomy. It spoke of quasi-contract, implied contract, money paid to the defendant's use, money had and received, quantum meruit and quantum valebat. These labels were procedural and remedial, not conceptually exact.

The contractual fiction was particularly important. Courts often said that the law implied a promise by the defendant to repay. This was never a genuine consensual promise. It was a technique by which assumpsit could be used to enforce a non-consensual obligation. The fiction obscured the distinction between obligations voluntarily undertaken and obligations imposed because retention of a benefit was unjust. That distinction is now fundamental. A restitutionary claim is not founded on the defendant's promise, unless there is in fact a contract. It is imposed by law.

Nineteenth- and early twentieth-century contract law, with its emphasis on freedom of contract and formal categories, often inhibited a general restitutionary principle. Recovery for payments under failed contracts was constrained by the doctrine of total failure of consideration. If the claimant had received any part of the stipulated performance, restitution was normally refused. This produced hard results where money was paid in advance but the defendant only partly performed. The law also took a restrictive view of mistakes of law, traditionally denying recovery where the payer had made a legal rather than factual error. Frustration produced another notorious difficulty. At common law, money paid before frustration could not be recovered if the consideration had not totally failed, and money due before frustration remained payable. Chandler v Webster exemplified this harshness. Fibrosa marked the judicial turning point, and the Law Reform (Frustrated Contracts) Act 1943 supplied a statutory scheme.

The modern law is usually dated from two developments. The first was intellectual. Scholars, especially Goff and Jones, Birks, Burrows and later Virgo, argued that English law contained an autonomous law of unjust enrichment. They insisted that cases formerly described as quasi-contract were neither contract nor tort, but a distinct source of obligations. The second was judicial. Lipkin Gorman confirmed unjust enrichment as a general principle of English law and recognised change of position as a defence. Woolwich created or confirmed a public-law restitutionary right to recover taxes paid pursuant to unlawful demands. Kleinwort Benson abolished the bar on recovery for mistake of law. Benedetti refined the measure of enrichment for services.

The result is a field that is both mature and unsettled. English law accepts unjust enrichment as a source of obligations, but it has not adopted a civilian-style general clause. It works through unjust factors rather than through a broad absence-of-basis test, although failure of basis has increasingly drawn English law towards the latter language. In Contract, this history matters because the old forms still leave traces. The phrase total failure of consideration appears in cases and textbooks, yet it can mislead students into analysing the matter as contractual consideration. The better approach is to ask whether the basis of the claimant's transfer, objectively understood, has failed sufficiently to justify restitution.

The orthodox structure is fourfold: enrichment; at the claimant's expense; unjust factor; absence of defence. This structure is not a mechanical incantation. Each question performs a separate limiting function.

First, enrichment. The defendant must have received something of value. Obvious enrichments include money, goods, services, discharge of a debt, release from liability, use of property and improvements to land or chattels. Money is incontrovertibly beneficial: a defendant cannot say that a payment into its hands was unwanted or worthless. Services and non-money benefits are harder. English law is cautious about imposing liability for unsolicited benefits because autonomy includes the freedom not to buy. A defendant may be enriched where the services were requested, freely accepted, necessary, incontrovertibly beneficial, or where the defendant had an opportunity to reject them but did not. In contractual settings, a request will often be decisive: if D asks C to perform work in anticipation of a contract, or accepts work under an ineffective contract, D may be enriched even if no enforceable promise to pay exists.

Secondly, the enrichment must be at the claimant's expense. The paradigm case is direct transfer: C pays D £10,000. But triangular arrangements are common in commercial contract. Banks, intermediaries, tax authorities, agents and trustees may stand between payer and recipient. English law has resisted a simple causal test. It asks whether the enrichment is sufficiently attributable to the claimant, often by identifying a transfer of value or a subtraction from the claimant's assets. Investment Trust Companies and Prudential Assurance show the difficulty where the immediate payer has passed an economic burden down a chain. Contract students should be alert to the difference between economic incidence and legal attribution.

Thirdly, there must be an unjust factor. English law normally requires the claimant to identify a recognised reason why retention is unjust. The principal contractual unjust factors are mistake, duress, undue influence, failure of basis, legal compulsion, necessity, incapacity and, in public authority cases, the Woolwich principle. Mistake covers payments made under a causative mistake of fact or law. Duress overlaps with the Week 8 doctrine but the remedial question may be restitution rather than rescission alone. Failure of basis is central: C confers a benefit on the basis that a state of affairs will exist, or that D will perform, and that basis fails.

The landmark cases trace a movement from procedural quasi-contract to a principled law of unjust enrichment, while preserving limits imposed by contract, statute and defences.

Moses v Macferlan is the canonical starting point. It treated money had and received as available where the defendant ought in justice to refund money. Its enduring importance is not that modern courts have adopted Lord Mansfield's broad moral language without qualification. They have not. Its importance is that it recognised a common law obligation to restore benefits independently of genuine consent. The case also explains why the older language of implied promise should be treated as historical form rather than analytical substance.

Fibrosa is central for Contract. The claimant paid an advance price for machinery to be delivered to Poland. War made performance illegal and the contract was frustrated. The House of Lords allowed recovery because there had been a total failure of consideration. The case undermined Chandler v Webster and prepared the ground for the 1943 Act. Its doctrinal lesson is that a payment made for a contractual performance may be recoverable when that performance wholly fails; its limitation is that the total failure requirement could produce arbitrary results.

Lipkin Gorman is the modern recognition case. A solicitor misappropriated client money and gambled it at the defendant casino. The firm recovered part of the money from the casino in unjust enrichment, subject to the casino's change of position defence. The House of Lords acknowledged unjust enrichment as a distinct principle and introduced change of position into English law. For Contract, the case is less about gambling than about structure: enrichment, at the claimant's expense, unjust retention, and defences.

Woolwich is a public law restitution case, but it is often examined because it expanded the catalogue of unjust factors. A building society paid tax demanded under regulations later held ultra vires. The House of Lords allowed recovery as of right. The decision cannot be reduced to mistake or duress; it rests on the constitutional principle that taxes unlawfully demanded should be repaid. It demonstrates the common law's capacity to recognise new unjust factors in controlled circumstances.

Kleinwort Benson abolished the old bar on recovery for mistake of law. Banks had paid money under interest rate swap agreements later held void. The House of Lords held that money paid under a mistake of law could be recovered. The case is essential because contractual invalidity often turns on law, not fact. If legal mistake were irrecoverable, many claims after void contracts would fail for no defensible reason.

Benedetti v Sawiris is the leading modern case on valuation of services. The claimant performed services in connection with a corporate acquisition without an enforceable contract fixing remuneration. The Supreme Court held that the enrichment was to be valued objectively by reference to the market value of the services, subject to principles of subjective devaluation and any relevant agreement on value. The case is indispensable in quantum meruit problems, especially where negotiations fail or no binding contract covers the work done.

Investment Trust Companies refined the at-the-expense-of requirement in a tax and VAT chain. The Supreme Court was cautious about allowing final consumers or investors to leapfrog intermediaries without a sufficient legal link. The case matters in contract because many payments occur through chains. The claimant must show not merely that it bore an economic burden, but that the defendant's enrichment was legally at its expense.

Together these cases supply the modern map. Fibrosa and the 1943 Act govern failed contractual performance; Lipkin Gorman supplies principle and defence; Kleinwort Benson expands mistake; Benedetti governs valuation; Woolwich and Investment Trust Companies show that unjust enrichment is responsive to public law and transactional structure, not only bilateral bargains.

See practice questions section below.

See further reading section below.