ABSTRACT
An ‘estoppel’ exists when, in consequence of some previous act or statement to which he is either a party or a privy,1 a person is precluded from afterwards showing the existence of a different state of affairs than that indicated by the previous act or statement.2 The rule is based on considerations of justice and public policy. It would be unjust to allow someone to do or say something, yet afterwards try to obtain an advantage by denying the validity of what he did earlier, or the truth of what he said earlier. It would be contrary to public policy to allow identical claims to be repeatedly litigated. However, estoppel cannot be used to authorise illegality.3 For example, if powers that are ultra vires are assumed by a person or body, estoppel cannot be used to authorise what has been done.4 Similarly, the courts have refused to allow an estoppel to prevent the application of the Moneylenders Acts.5 It is a matter of interpretation in each case whether a statute has made a transaction absolutely illegal or void, or merely voidable; in the latter case, it may be possible to plead estoppel successfully.6
