Where a contravention of a provision of this Act or of regulations thereunder for which a person is, by virtue of the last foregoing section, liable on conviction to a penalty was due to an act or default of another person, then, whether proceedings are or are not taken against the first-mentioned person, that other person may be charged with, and convicted of, the contravention, and shall, on conviction, be liable to the same punishment as that to which the first-mentioned person is, on conviction, liable.