Estoppel

Estoppel is an equitable remedy that prevents a person from doing some otherwise legal act contrary to his own previous assertion or act. It is usually exercised to prevent an otherwise-legal action.

Courts recognise that on occasion it will be appropriate to stop someone from taking an action that would otherwise be consistent with their legal rights, if someone else has relied upon an assertion or an act that they would not enforce their rights.

For example, Bob buys a house off Richard, and makes a verbal promise to Richard that he would honour Sarah's tenancy in that house. The contract signed promises vacant possession (i.e. no tenancy) and Bob has made no contract with Sarah. Nonetheless a court will not enforce Bob's right to unilaterally terminate the tenancy because it is inconsistent with his earlier actions IF (and only if) Sarah has relied upon Bob's promise. In legal vernacular, Bob is estopped from denying a tenancy to Sarah.

See also: promissory estoppel