20. (1) Notwithstanding anything contained in sections 6,7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17 and 18, in any prosecution for the sale of any article of food in contravention of any of the provisions of those sections relating to such article, it shall be a defence for the seller to prove - (a) that he purchased such article as being of a nature substance or quality which would entitle him to sell it and with a written warranty to that effect, and (b) that, at the time of the sale to which the prosecution relates, he had no reason to suppose that the article was not of such a nature, substance or quality, and that it was then in the same condition as when he purchased it: Provided that a warranty given by a person who is not a resident in Bangladesh shall not be a defence unless the seller strictly proves to the satisfaction of the Court that he had taken reasonable steps to ascertain, and did in fact believe in, the correctness of the statement contained in the warranty. (2) Notwithstanding anything contained in any other law for the time being in force, no evidence relating to a warranty alleged under clause (a) of sub-section (1) shall be admissible on behalf of the seller unless, within seven days of the date of service upon him of any process issued by a Court for his attendance therein, he has sent- (a) to the complainant a copy of the warranty, together with a written notice stating that he intends to rely upon the warranty and specifying the name and address of the person from whom he received it, and (b) to the person from whom he received the warranty, a notice of his intention to rely upon it. (3) No person, whether as a principal or as an agent, shall give to a purchaser, in respect of any article of food, any warranty in writing which is false or which he has reason to believe to be false.