Restitution and unjust enrichment

Restitution and unjust enrichment sit at the edge of the Year 1 Contract Law course. The topic is not primarily concerned with enforcing bargains. It asks a different question: when one party has received money, services, a discharge of liability, or another benefit, in circumstances where the law regards retention as unjust, what response should follow? The answer is usually a personal obligation to make restitution of the value received. It may occasionally be proprietary or subrogatory, but the ordinary first-year contract focus is personal restitution.

This matters because the contract syllabus otherwise tends to be organised around formation, vitiation, discharge and remedies for breach. Restitution cuts across each. A contract may be void for mistake, avoided for misrepresentation, set aside for duress or undue influence, discharged for frustration, terminated after breach, or never concluded for uncertainty. In all these situations, there may have been transfers before the legal problem was discovered. Damages cannot always help: damages compensate loss caused by breach; restitution reverses unjust enrichment. Specific performance compels performance of a promise; restitution responds to enrichment already received. Reliance damages compensate wasted expenditure; restitution values the defendant’s gain, not necessarily the claimant’s loss.

The modern English law of unjust enrichment is commonly expressed through four questions: has the defendant been enriched; was the enrichment at the claimant’s expense; was the enrichment unjust; and is there any applicable defence? That scheme is associated with the modern law after Lipkin Gorman v Karpnale Ltd and has been repeated in later Supreme Court authority. It is a useful exam structure, but it is not a substitute for legal reasoning. Each question contains difficulty. Money is plainly an enrichment, but services are harder because a person may deny that they wanted them. Enrichment must ordinarily be at the claimant’s expense, but indirect enrichment has generated controversy. The unjust element is not a free moral discretion: English law works through recognised unjust factors, such as mistake, duress, failure of basis and sometimes necessity. Defences, especially change of position, prevent unjust enrichment from becoming strict liability without limits.

For Durham first-year purposes, the topic should be treated as a bridge between contract doctrine and private-law method. It tests whether students can distinguish causes of action and remedies with precision. A good answer does not say simply that the defendant has been unjustly enriched. It identifies the legal route by which a contract has failed, been avoided, or allocated the risk; it then asks whether restitution is consistent with that route. In contract problems, the most important warning is that restitution cannot be used to rewrite a valid bargain merely because it has become unprofitable. If the parties made an enforceable contract which allocates a risk, unjust enrichment normally gives way to that allocation. Restitution is powerful, but it is not a general jurisdiction to impose fairness after the event.

English restitution law has emerged from procedural history, not from a single code or statute. The older forms of action used the language of implied promise. A claimant brought indebitatus assumpsit and alleged that the defendant had promised to repay money had and received, money paid, or a quantum meruit. The promise was often fictional. The law was not enforcing an actual agreement; it was compelling restoration because retention of the benefit was treated as unjust. That history matters because it explains why restitutionary claims were long misdescribed as quasi-contractual. They looked contractual in form, but they were not contractual in substance.

Moses v Macferlan is the classic eighteenth-century source. Lord Mansfield described the action for money had and received in broad equitable language. Later lawyers treated that language with caution, because it could be read as inviting an unconfined discretion to do justice. Nineteenth- and early twentieth-century English law became more restrictive. The dominance of contract, the forms of action, and suspicion of vague equitable language produced a fragmented set of claims rather than a coherent law of unjust enrichment.

Two developments changed the landscape. The first was the recognition that the old implied-contract explanation was untenable. If a contract is void, or if money is paid under a mistake, it is artificial to say that the defendant promised to repay. In Sinclair v Brougham, the House of Lords rejected some implied-contract reasoning in a way that produced doctrinal difficulty. The second was the influence of juristic writing, especially the work later associated with Goff and Jones and with Peter Birks. Their project was to show that disparate claims could be organised around a common principle: unjust enrichment at another’s expense.

Fibrosa Spolka Akcyjna v Fairbairn Lawson Combe Barbour Ltd is central in the contract syllabus. A buyer paid in advance for machinery, but wartime frustration prevented performance. The House of Lords permitted recovery of the advance payment on total failure of consideration. Lord Wright explicitly recognised the need for legal remedies against unjust enrichment. The case also exposed the limits of the common law, because it required total failure. Parliament responded with the Law Reform (Frustrated Contracts) Act 1943, which gives a discretionary statutory regime for recovery of money and non-money benefits after frustration.

The decisive modern moment was Lipkin Gorman v Karpnale Ltd. A solicitor misappropriated client money and gambled it at a casino. The House of Lords recognised unjust enrichment as an independent source of obligation and also recognised change of position as a defence. From that point, unjust enrichment could no longer sensibly be treated as a miscellaneous appendix to contract. Subsequent cases refined particular elements: Banque Financiere on subrogation, Sempra Metals and Deutsche Morgan Grenfell on mistake and interest, Benedetti on valuation of services, and Investment Trust Companies on the structure and limits of the cause of action.

The historical lesson is therefore double. Restitution is not new: many of its actions are old. But unjust enrichment as an organising principle is modern. In a first-year exam, that matters because the language of quasi-contract should be handled carefully. It may appear in older authorities, but the modern analysis is not that the court invents a contract. It is that the law imposes a non-consensual duty to restore a benefit where a recognised ground of restitution is made out and no defence applies.

The starting point is the four-stage inquiry. First, has the defendant been enriched? Secondly, was the enrichment at the claimant’s expense? Thirdly, was the enrichment unjust? Fourthly, does a defence defeat or reduce the claim? This structure is now orthodox, but it must be applied with attention to contract.

Enrichment is normally straightforward where the defendant has received money. Money is the paradigm benefit because it is universally useful and does not raise problems of unwanted receipt. If D receives £5,000 from C, D is enriched by £5,000 unless a recognised reason reduces the value. Enrichment may also consist in discharge of a debt, use of property, services, or improvements. Services are more difficult. A defendant can say: I did not ask for them; I did not want them; and they cannot now be returned. English law avoids imposing liability for officious intervention. It therefore uses controls such as request, free acceptance, subjective devaluation and incontrovertible benefit.

Subjective devaluation means that a defendant is generally entitled to say that a benefit is worth less to them than its market value. If C paints D’s house without request, D is not necessarily enriched by the market price of painting. The law protects autonomy: people should not be forced to buy benefits. But subjective devaluation can be displaced. If D requested the service, freely accepted it knowing that payment was expected, or received an incontrovertible benefit such as discharge of an unavoidable liability, the objective value may be recoverable. Benedetti v Sawiris is the leading modern authority on valuation. The prima facie measure is objective market value, subject to evidence that the defendant valued the benefit less or more in legally relevant circumstances.

The landmark cases show both the breadth and the discipline of unjust enrichment. Fibrosa remains the essential contract case. It arose from a frustrated contract and permitted recovery of an advance payment where the expected performance wholly failed. Its significance is not merely its result; it repudiated the fiction that restitution depends on an implied promise and recognised unjust enrichment as a juristic concern. It also prompted the 1943 Act, which now supplies the statutory regime for many frustrated contracts.

Lipkin Gorman supplies the modern foundation. The claimant firm’s money had been stolen by a partner and lost at the defendant casino. The House of Lords held that the casino was enriched by receipt of the money, that the enrichment was at the firm’s expense, and that the claim lay in restitution. Crucially, the House also recognised change of position. The casino had paid out some winnings in good faith and was not required to repay the full gross receipts. Lipkin Gorman therefore establishes both principle and limitation.

Banque Financiere illustrates that unjust enrichment can generate sophisticated remedies such as subrogation. Money was advanced to assist a refinancing on the mistaken assumption that security would be effective. The House of Lords allowed subrogation to prevent the defendants gaining an unintended priority benefit. The case is important because it shows that unjust enrichment is not confined to simple repayment. It can explain equitable techniques where the substance is reversal of enrichment.

Deutsche Morgan Grenfell and Sempra Metals are central to mistake of law and time value of money. Older English law drew a sharp distinction between mistake of fact and mistake of law. That distinction has been rejected. Payments made under a mistake of law can be recoverable, though limitation and statutory context may matter. Sempra Metals also recognised that the use value of money can itself be an enrichment and allowed compound interest in restitutionary form, although later case law has refined the remedial route.

Benedetti is indispensable on services. The claimant introduced the defendant to a valuable corporate opportunity and claimed a very large reward. The Supreme Court held that valuation starts with objective market value, not the claimant’s expectations or the defendant’s eventual profit. Evidence may show subjective devaluation or a higher subjective value, but the analysis must remain disciplined. This is particularly useful in problem questions involving informal negotiations, failed contracts, or services rendered in anticipation of agreement.

Investment Trust Companies v HMRC demonstrates restraint. The Supreme Court accepted the standard four-stage structure but refused to impose an over-expansive personal restitutionary liability. In complex statutory tax arrangements and indirect payment chains, the court asks whether the enrichment is truly at the claimant’s expense and whether the claim would disrupt the relevant legal scheme. This is a valuable corrective to superficial answers which treat unjust enrichment as a general fairness jurisdiction.

Taken together, the cases show the modern law’s pattern. The courts recognise unjust enrichment as an independent source of obligations; they insist on structured elements; they permit flexible responses where justified; but they guard against undermining contract, statute, and settled allocation of risk.

See practice questions section below.

See further reading section below.