However, the most significant part of the judgment is obiter dictum as it relates to hypothetical facts; that is, the landlord did not seek repayment of the full wartime rent.

Denning J held estoppel to be applicable if a promise was made which was intended to create legal relations and which, to the knowledge of the person making the promise, was going to be acted on by the person to whom it was made and which was in fact so acted on.High Trees House Ltd leased a block of flats in Battersea, London from Central London Property Trust Ltd.

On 21 September 1945, Central London Property wrote to High Trees to request a return to the full rent of £2,500 and claiming arrears of £7,916 for the period since 1940.

Based on previous judgments as Hughes v Metropolitan Railway Co, Denning J held that the full rent was payable from the time that the flats became fully occupied in mid-1945.

Being obiter dicta and in a court of first instance this was doubly not a binding precedent, yet it essentially created the doctrine of promissory estoppel.

If I were to consider this matter without regard to recent developments in the law, there is no doubt that had the plaintiffs claimed it, they would have been entitled to recover ground rent at the rate of £2,500 a year from the beginning of the term, since the lease under which it was payable was a lease under seal which, according to the old common law, could not be varied by an agreement by parol (whether in writing or not), but only by deed.

In each case the court held the promise to be binding on the party making it, even though under the old common law it might be difficult to find any consideration for it.

The courts have not gone so far as to give a cause of action in damages for the breach of such a promise, but they have refused to allow the party making it to act inconsistently with it.

At this time of day however, when law and equity have been joined together for over seventy years, principles must be reconsidered in the light of their combined effect.

I find that the conditions prevailing at the time when the reduction in rent was made, had completely passed away by the early months of 1945.

I am satisfied that the promise was understood by all parties only to apply under the conditions prevailing at the time when it was made, namely, when the flats were only partially let, and that it did not extend any further than that.

I therefore give judgment for the plaintiff company for the amount claimed.Advances have been made in promissory estoppel since its inception in High Trees to create a new inroad into the rule in Pinnel's case that an agreement to accept part payment of a debt in full satisfaction of it is unenforceable for want of consideration.

Denning commented that such an agreement should now be enforceable under the doctrine of promissory estoppel, and indeed the plaintiff did not seek the full debt on the basis of what was fair and, perhaps, thought was the law.

Lady Justice Arden in Collier v P & MJ Wright (Holdings) Ltd (2007)[1] accepted in principle that High Trees could be used to extinguish a creditor's right to full payment of a debt in such circumstances.