(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.

   (2)  If, in any suit in which a contract or other instrument is sought to be rectified under sub-section (1), the court finds that the instrument, through fraud or mistake, does not express the real intention of the parties, the court may in its discretion, direct rectification of the instrument so as to express that intention, so far as this can be done without prejudice to rights acquired by third persons in good faith and for value.

   (3)  A contract in writing may first be rectified, and then if the party claiming rectification has so prayed in his pleading and the court thinks fit, may be specifically enforced.

   (4)  No relief for the rectification of an instrument shall be granted to any party under this section unless it has been specifically claimed:

   Provided that where a party has not claimed any such relief in his pleading, the court shall, at any stage of the proceeding, allow him to amend the pleading on such terms as may be just for including such claim.