18. (1) No person shall, directly or indirectly and whether by himself or by any other person acting on his behalf, with any article of food sold by him, give to the purchaser a label, whether attached to or printed on the container in which such article is sold or not, which falsely describes that article or is otherwise calculated to mislead as to its nature, substance or quality. (2) In any prosecution under this section, it shall not be a defence to allege that the person who gave such a label had no knowledge of, and could not with reasonable diligence have ascertained, its character.