ABSTRACT
In Chapter 10 we saw that sometimes restitution is desired although none of the usual unjust factors are available. Restitution is based on policy in those cases, and it was argued that it is desirable to identify and spell out that policy as clearly as possible. Most of the cases looked at in that chapter also involved void contracts. This was explained on the basis that the policy leading to the nullity or voidability of the contract is in some, but not all, cases carried through to restitution. In those cases the policy is best served by unwinding an executed transaction. Merely rendering an executory transaction unenforceable is not enough. Sometimes, however, there is no underlying transaction or obligation at all, or it is wholly void, but nevertheless restitution is not a desirable consequence. A system which makes restitution available on the basis of nullity as such, or which bases restitution on mistake of law widely interpreted, must take care to keep restitution within acceptable bounds. One way to do this, of course, is by putting in place wide and robust defences, particularly a strong change of position defence. It will be suggested in the next chapter that this may well be the only option for English law following Westdeutsche and Lincoln, at least in the short to medium term.
