(iii) Imposition of Conditions
The court might be prepared to make the application of the defence conditional on the defendant accepting that he or she would return that part of the benefit to the claimant in respect of which his or her circumstances had not changed, although Slade LJ left open whether the court had jurisdiction to obtain such an undertaking from the defendant.
(iv) Shifting the Burden of Proof
Cumming-Bruce LJ in Avon CC v Howlett47 suggested that the burden of proof might be shifted, so that once the defendant has shown that he or she had suffered some detriment in reliance on the claimant’s representation, the claimant must then prove that the defendant’s circumstances changed only in respect of part of the benefit which he or she received. But such a recommendation is unlikely to work in practice, since the claimant is unlikely to know, let alone be able to prove, to what extent the defendant’s circumstances had actually changed.
-  Ltd  AC 670, 688, but in that case such an undertaking was voluntarily proferred by the defendant.