Promissory estoppel

Promissory estoppel is an equitable doctrine which in some instances can stop a person going back on a promise which is not supported by consideration. Promissory estoppel was developed by an obiter statement by Denning J (as he then was) in Central London Property Trust Ltd v High Trees Ltd [1947] KB 130 (Case summary). Denning J based the doctrine on the decision in Hughes v Metropolitan Railway (1876-77) L.R. 2 App. Cas. 439 (Case summary). The House of Lords affirmed the existence of promissory estoppel in contract law in Tool Metal Manufacturing v Tungsten [1955]
Requirements of promissory estoppel:
1. A pre-existing contract or legal obligation which is then modified
2. There must be a clear an unambiguous promise
3. Change of position
4. It must be inequitable to allow the promisor to go back on their promise