Mistaken payments return to the High Court: Commissioner of Revenue v. Royal Insurance

Beginning with its momentous decision in Pavey & Matthews Pty Ltd v Paul,' the High Court has accepted that the concept of unjust enrichment underlies the law of restitution.2 That concept commonly is said to be comprised of four elements: (i) an enrichment to the defendant, (ii) received at the plaintiffs expense, (iii) acquired as the result of an unjust factor, (iv) in the absence of circumstances supporting a defence. Those elements are not analysed with equal regularity in the case law. Difficulties occasionally arise with respect to the first element, given the diverse nature of wealth and the relative novelty of the concept of unjust enrichment, and the courts have yet to determine conclusively which benefits count for the purposes of the law of restitution. 3 The third element is examined more frequently, indeed, in many instances, the existence or non-existence of a recognised unjust factor is the only contentious issue in a restitutionary action.4