(1) When, through fraud or a mutual mistake of the parties, a contract or other instrument in writing (not being the articles
of association of a company to which the Companies Act, 1956 (1 of 1956 ), applies) does not express their real intention, then-
(a) either party or his representative in interest may institute a suit to have the instrument rectified; or
(b) the plaintiff may, in any suit in which any right arising under the instrument is in issue, claim in his pleading that the instrument be rectified; or
(c) a defendant in any such suit as is referred to in clause (b), may, in addition to any other defence open to him, ask for rectification of the instrument.