This section applies to—
(a) any offence under this Act to which it is applied by column 7 of Part I of Schedule 4 to this Act; and
(b) any offence under section 77(7) of the Road Traffic Regulation Act 1967 or punishable by virtue of section 78A of that Act.
Subject to the following provisions of this section and to the provisions of paragraphs 5, 6 and 7 of Part IV of the said Schedule 4, where a person is prosecuted for an offence to which this section applies he shall not be convicted unless either—
(a) he was warned at the time the offence was committed that the question of prosecuting him for some one or other of the offences to which this section applies would be taken into consideration ; or
(b) within fourteen days of the commission of the offence a summons (or, in Scotland, a complaint) for the offence was served on him ; or
(c) within the said fourteen days a notice of the intended prosecution specifying the nature of the alleged offence and the time and place where it is alleged to have been committed, was—
(i) in the case of an offence against section 17 or 18 of this Act, served on him,
(ii) in the case of any other offence, served on him or on the person, if any, registered as the keeper of the vehicle at the time of the commission of the offence;
and the notice shall be deemed for the purposes of paragraph (c) above to have been served on any person if it was sent by registered post or recorded delivery service addressed to him at his last known address, notwithstanding that the notice was returned as undelivered or was for any other reason not received by him.
The requirement of subsection (2) above shall in every case be deemed to have been complied with unless and until the contrary is proved.
Failure to comply with the requirement of subsection (2) above shall not be a bar to the conviction of the accused in a case where the court is satisfied—
(a) that neither the name and address of the accused nor the name and address of the registered keeper, if any, could with reasonable diligence have been ascertained in time for a summons or, as the case may be, a complaint to be served or for a notice to be served or sent in compliance with the said requirement; or
(b) that the accused by his own conduct contributed to the failure.