21.—(1) In proceedings against a person for an offence under regulation 18, it is a defence for the person to prove that all reasonable precautions were taken and due diligence was exercised to avoid committing the offence.
(2) However, where the defence provided by paragraph (1) involves an allegation that the commission of the offence was due to the act or default of another person, a person (“A”) is not, without leave of the court, entitled to rely on that defence unless A has served on the prosecutor a notice in writing in accordance with paragraph (3) giving such information identifying or assisting in the identification of that other person as was then in A’s possession.
(3) The notice must be served—
(a)at least seven clear days before the hearing (or, in Scotland, the trial diet), and
(b)where A has previously appeared before a court in connection with the alleged offence, within one month of A’s first such appearance.