The historical core of the law of unjust enrichment consists of the
quasi-contractual actions of
money had and received, money paid to the defendant's use,
quantum meruit and quantum valebat. These personal
common law actions generated an obligation on the part of the defendant to give
restitution of a gain acquired at the expense of the plaintiff. This liability was
strict and independent of any wrongdoing on the part of the recipient. Change of position provides a defence to a defendant where it would be inequitable to compel him or her to make restitution. The defence was recognised as part of the
English law of unjust enrichment by Lord Goff in
Lipkin Gorman v Karpnale Ltd [1991] 2 AC 548. ==Cases & Materials==