Changes in the law do not take effect retrospectively. Willes J explained the policy underpinning this principle in Phillips v Eyre (1870) LR 6 QB 1 at 23: retrospective legislation was “contrary to the general principle that legislation by which the conduct of mankind is to be regulated ought, when introduced for the first time, to deal with future acts, and ought not to change the character of past transactions carried on upon the faith of the then existing law”. Notwithstanding this principle, there was no doubt that a legislator may introduce laws which alter rights and obligations in relation to events which have already taken place. The question was always whether, contrary to the presumption against retrospectivity, the law in fact had that effect.