The claimant had entered into an oral (unenforceable) agreement with defendants in connection with the redevelopment of their property. The defendants’ unconscionable behaviour in withdrawing from the agreement once planning permission for the redevelopment had been obtained did not result in a proprietary estoppel or a constructive trust in favour of the claimant.
Lord Scott: Proprietary estoppel is just a species of the ordinary form of estoppel: It prevents A from denying that which he represented to be true. Therefore it cannot be a means of acquiring rights itself here, since all the defendant is estopped from denying is the existence of an unenforceable agreement.
Lord Walker: The courts should be slow to introduce uncertainty into commercial transactions by overready use of equitable concepts such as fiduciary obligations and equitable estoppel. Proprietary estoppel can be a means of acquiring rights, but the claimant must have an actual ‘expectation’ of acquiring rights, rather than just a ‘mere hope’, as here. Hence the agreement had to have been ‘binding and irrevocable’.