Proceedings for an offence under these Regulations which is triable only summarily may be brought within the period of 12 months beginning with the date on which evidence sufficient in the opinion of the prosecutor to justify the proceedings comes to the prosecutor's knowledge.

But such proceedings may not be brought by virtue of paragraph (1) more than 3 years after the commission of the offence.

A certificate signed by the prosecutor as to the date on which the evidence in question came to the prosecutor's knowledge is conclusive evidence of the date on which it did so; and a certificate to that effect and purporting to be so signed is to be treated as being so signed unless the contrary is proved.