20.—(1) Subject to paragraphs (2) and (3), in any proceedings for an offence under Article 31 of the 1978 Order for a contravention of regulations 13 or 15, or of Articles 5, 9(3) or 9(4) of the Precursors Regulation (by virtue of regulation 18), it is a defence for the person charged (“P”) to prove—
(a)that the commission of the offence was due to the act or default of another person, not being one of P's employees (the “other person”); and
(b)that P took all reasonable precautions and exercised all due diligence to avoid the commission of the offence.
(2) P is not, without the leave of the court, entitled to rely on the defence in paragraph (1) unless, not less than 7 days before the hearing, P has served on the prosecutor a notice in writing giving such information identifying or assisting in the identification of the other person as was then in P's possession.
(3) For the purpose of enabling the other person to be charged with and convicted of the offence by virtue of Article 34 of the 1978 Order, a person who establishes a defence under this regulation shall nevertheless be treated for the purposes of that Article as having committed the offence.