6.—(1) If the person who has received a notice of intent does not discharge liability for the penalty within the 28 day period referred to in paragraph 4, the authorised officer may serve a final notice imposing a fixed monetary penalty.
(2) The authorised officer may not serve a final notice on a person where the authorised officer is satisfied that the person would not, by reason of any defence, be liable to be convicted of the offence to which the notice relates.
(3) An authorised officer who serves a final notice imposing a fixed monetary penalty may not serve any other notice under these Regulations in relation to the offence.