A doctrine of equity that a contract required to be evidenced in writing will still be enforceable even if it is not so evidenced provided that one of the parties does certain acts by which the contract is partly performed. For an act to bring the doctrine into play (i.e. a sufficient act of part performance) that act must be performed by the person alleging the contract to exist and must relate unequivocally to the contract; an example would be taking possession of property alleged to have been sold (under a contract entered into before 21 September 1989) to the person who takes possession. It is unclear whether mere payment of money is a sufficient act of part performance.
This doctrine applied primarily to contracts for the sale of land. However, such contracts entered into on or after 21 September 1989 are required, under the Law of Property (Miscellaneous Provisions) Act 1989, to be in writing (not merely evidenced in writing) if they are to be valid. Acts of part performance will not, as such, validate an unwritten land contract, although they may, in particular circumstances, give rise to a proprietary estoppel or a constructive trust.