ABSTRACT
Denning LJ: Much as I am inclined to favour the principle of the High Trees case, it is important that it should not be stretched too far, lest it should be endangered. It does not create new causes of action where none existed before. It only prevents a party from insisting on his strict legal rights when it would be unjust to allow him to do so, having regard to the dealings which have taken place between the parties. That is the way it was put in the case in the House of Lords which first stated the principle – Hughes v Metropolitan Railway Co – and, in the case in the Court of Appeal which enlarged it – Birmingham and District Land Co v London and North Western Railway Co. It is also implicit in all the modern cases in which the principle has been developed. Sometimes it is a plaintiff who is not allowed to insist on his strict legal rights. Thus, a creditor is not allowed to enforce a debt which he has deliberately agreed to waive if the debtor has carried on business or in some other way changed his position in reliance on the waiver: Sometimes it is a defendant who is not allowed to insist on his strict legal rights. His conduct may be such as to debar him from relying on some condition, denying some allegation, or taking some other point in answer to the claim. Thus, a government department, who had accepted a disease as due to war service, were not allowed afterwards to say it was not, when the soldier, in reliance on the assurance, had abstained from getting further evidence about it: Robertson v Minister of Pensions. A buyer who had waived the contract date for delivery was not allowed afterwards to set up the stipulated time as an answer to the seller: Charles Rickards Ltd v Oppenheim. A tenant who had encroached on an adjoining building, asserting that it was comprised in the lease, was not allowed afterwards to say that it was not included in the lease: JF Perrott & Co Ltd v Cohen. A tenant who had lived in a house rent free by permission of his landlord, thereby asserting that his original tenancy had ended, was not afterwards allowed to say that his original tenancy continued: Foster v Robinson. In none of these cases was the defendant sued on the promise, assurance, or assertion as a cause of action in itself. He was sued for some other cause, for example, a pension or a breach of contract, or possession, and the promise, assurance, or assertion only played a supplementary role, though, no doubt, an important one. That is, I think, its true function. It may be part of a cause of action, but not a cause of action in itself. 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 at his word and acted on it, the one who gave the promise or assurance cannot afterwards be allowed to revert to the previous legal relations as if no such 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.
