Estoppel
Also called: Promissory estoppel, estoppel by representation
A rule that prevents a person from going back on a clear promise or statement that another person has relied on to their detriment.
Definition
Estoppel is a broad equitable doctrine that prevents ("estops") a party from asserting a position that contradicts a previous representation or promise, where another party has relied on that representation and would suffer detriment if the first party were allowed to resile. There are several forms: estoppel by representation (a statement of existing fact); promissory estoppel (a clear promise to vary legal rights, as in <em>Central London Property Trust v High Trees House</em> [1947] KB 130); and proprietary estoppel (a promise about land rights acted upon to the promisee's detriment). In England and Wales, promissory estoppel operates as a shield (preventing enforcement of strict legal rights) rather than as a sword (creating new rights), except in proprietary estoppel cases.
In practice
If someone — a landlord, employer, or commercial counterparty — made you a clear and unambiguous promise, and you acted on it to your financial or practical detriment, you may be able to argue estoppel even without a formally varied contract. Estoppel claims require careful evidence: note the exact words used, when, in front of whom, and what you then did in reliance. Courts are sceptical of vague informal assurances.