(vi) The Defence Operates Pro Tanto
The defence will only be applicable to the extent that the benefit has been transferred to the principal. So, for example, if the agent receives ?1,000 from the claimant by mistake and pays ?750 of this to the principal, the agent will remain liable to repay the outstanding ?250 to the claimant.
(vii) The Defence is Available to All Restitutionary Claims
The agent’s defence is applicable regardless of the type of restitutionary claim brought by the claimant. So, for example, the defence has succeeded where the claim has been founded on the reversal of unjust enrichment, where the ground of restitution was spontaneous mistake,[1] induced mistake,[2] and duress of goods,[3] [4] though in the latter two cases the defence only succeeded because the agent was unaware of the principal’s wrongdoing. Millett J recognized in Agip (Africa) Ltd v Jackson81 that the defence would also succeed where the claimant brought an action for money had and received founded on the vindication of proprietary rights. But in the same case Millett J held that there was no scope for the defence to operate where the claim was founded on the equitable action for unconscionable receipt.82 This distinction between Common Law and equitable claims, which are founded on the same principle of the vindication of property rights, presumably arises from the fact that the agent in the action for unconscionable receipt is implicated in wrongdoing.
