In the absence of a bargain, promissory estoppel and moral obligation are the only grounds upon which common law courts enforce promises. The principle of promissory estoppel came into existence to preclude the necessity for consideration in cases where parties are already bound contractually with each other and one of them promises to waive, alter or suspend its strict legal rights. The terms mean: Promissory; about a promise, assurance and Estoppel; comes from Latin, to stop. A clear cut definition for the doctrine was expressed by Denning LJ in Combe v Combe (1951) 2 KB 215 (CA).
The principle, as I understand it, is that, where one party has, by his words or conduct, made to the other a promise or assurance which was intended to affect the legal relations between them and to be acted on accordingly, then, once the other party has taken him his word and acted on it, the one who gave the promise or assurance had been made by him, but he must accept their legal relations subject to the qualification which he himself has so introduced, even though it is not supported in point of law by any consideration but only by his word.
The law on this principle derives from the case Central London Property Trust Ltd v High Trees House Ltd (1947) KB 130. The plaintiffs were the owners of a block of flats in London, which they rented to the defendants at a rent of £2,500 pa. Following the outbreak of the Second World War in 1939, the defendants were unable to find sufficient tenants to take the flats, because of the large numbers of people leaving London. As a result the plaintiffs agreed that, in the circumstances, the rent could be