(4) A fixed penalty notice must—  (5) Subject to paragraph (7), whatever other method may be specified under paragraph (4)(e),  payment of a fixed penalty may be made by pre-paying and posting to the person whose name is  stated under paragraph (4)(d), at the stated address, a letter containing the amount of the penalty  (in cash or otherwise).  (6) Where a letter is sent as described in paragraph (5), payment is regarded as having been  made at the time at which that letter would be delivered in the ordinary course of post.  (7) Paragraph (5) does not apply in the case of—  (8) In any proceedings, a certificate that—  is evidence of the facts stated.  (9) For the purposes of this regulation—  (a) give reasonably detailed particulars of the circumstances alleged to constitute the offence;  (b) state the period during which (because of paragraph (3)(a)) proceedings will not be taken  for the offence;  (c) specify the amount of the fixed penalty in accordance with Schedule 14;  (d) state the name and address of the person to whom the fixed penalty may be paid; and  (e) specify permissible methods of payment.  (a) an offence under regulation 19(7); or  (b) and offence under regulation 19(14) (obstruction) in relation to an offence under  regulation 19(7).  (a) purports to be signed by or on behalf of the designated officer; and  (b) states that the payment of a fixed penalty was, or was not, received by the date specified  in the certificate,  (a) other than in relation to an operator offence, “authorised person” means—  (i) a constable,  (ii) an immigration officer, but only in relation to the issue of a fixed penalty notice in  respect of an information offence or an offence described in regulation 19(1)(a), (b),  (c), (g), (h), (i), (j), (5) and (6), or  (iii) a person designated by the Secretary of State for the purposes of this regulation;  (b) in relation to an operator offence, “authorised person” means—  (i) in relation to passengers arriving by sea, the Secretary of State for Transport,  (ii) in relation to passengers arriving by air, the Civil Aviation Authority,  (iii) in relation to passenger arriving by rail, the Office of Rail and Road;  (c) “the designated officer” means—  (i) in relation to an offence other than an operator offence, an officer designated by the  Secretary of State for the purposes of this regulation,  (ii) in relation to an operator offence, the authorised person;  (d) “operator offence” means an offence—  (i) under regulation 19(7),  (ii) under regulation 19(13), or  (iii) under regulation 19(14) (obstruction) in relation to a function relating to an offence  under regulation 19(7).  27