Unjust enrichment
Unjust enrichment is the principle that a person who has been enriched at another's expense, in circumstances the law treats as unjust, must make restitution. The framework asks four questions: was the defendant enriched, at the claimant's expense, unjustly, and are there defences?
Last reviewed 14 June 2026
The four-question framework was confirmed in Banque Financière de la Cité v Parc (Battersea) Ltd and Benedetti v Sawiris: (1) enrichment, (2) at the claimant's expense, (3) an “unjust factor” (such as mistake, failure of consideration, or duress), and (4) defences (such as change of position).
It underpins restitutionary claims such as the recovery of money paid by mistake (Kelly v Solari) and money paid under a contract whose consideration has wholly failed.
Key cases
- Banque Financière de la Cité v Parc (Battersea) Ltd [1999] 1 AC 221
- Benedetti v Sawiris [2013] UKSC 50
- Kelly v Solari (1841) 9 M & W 54
Frequently asked questions
What are the elements of unjust enrichment?
Four questions: was the defendant enriched; at the claimant's expense; was it unjust (an “unjust factor”); and are there defences such as change of position?
What is an example of unjust enrichment?
Recovering money paid under a mistake (Kelly v Solari), or money paid under a contract whose consideration has wholly failed.