Sch 3 para 21
In any proceedings for an offence under this Act a document produced by one of the parties to the proceedings and purporting to be a certificate issued under paragraph 19 of this Schedule shall be sufficient evidence of the facts stated in the document, unless the other party requires that the person who issued the certificate shall be called as a witness; and, in any proceedings in Scotland, if that person is called as a witness, his evidence shall be sufficient evidence of those facts.