[21. (1) Where in an election petition a declaration that any candidate other than the returned candidate has been duly elected is claimed, the returned candidate or any other party may give evidence to prove that the election of such other candidate would have been void if he had been the returned candidate and a petition had been presented calling in question his election:
Provided that the returned candidate or such other party shall not be entitled to give such evidence unless he has within twenty-one days from the date of the service upon his of the notice of the election petition, given notice to the election tribunal of his intention to do so and has also deposited the security prescribed in the case of an election petition questioning the election of a member.
(2) Every notice referred to in sub-section (1) shall be accompanied by a statement of ground or grounds and of materials facts and full particulars required by section 20 in the case of an election petition and shall be signed and verified in like manner. ]