RESTITUTION WITHOUT ENRICHMENT
Although it seems obvious that if the claimant is to obtain restitutionary relief by virtue of the defendant’s unjust enrichment it must be established that the defendant has indeed been enriched, there are two situations where it might be possible to conclude that the claim for restitution should succeed even though the defendant has not been enriched.
(A) THE DEFENDANT IS ESTOPPED FROM DENYING THE ENRICHMENT
(i) The Function of Estoppel
Although the defendant may not have received an objective benefit, it might still be possible to show that the defendant has been enriched where he or she is estopped from asserting that he or she has not received a benefit at the claimant’s expense. If estoppel is being used to establish enrichment, it does not automatically establish the cause of action, since it will still be necessary for the claimant to establish that one of the recognized grounds of restitution is applicable. Rather, the function of the estoppel is simply to enable the claimant to pursue a restitutionary cause of action by negating one of the required elements of that action.
-  See Brandon LJ in Amalgamated Investment and Property Co Ltd v Texas Commerce International BankLtd  QB 84, 131-2.