s 20 Proceedings for summary offences .
(1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (2) Proceedings for a summary offence under this Part may be brought within a period of six months from the date on which evidence sufficient in the opinion of the prosecutor to warrant the proceedings came to his knowledge; but no such proceedings shall be brought by virtue of this section more than two years after the commission of the offence. (3) For the purpose of this section a certificate signed by or on behalf of the prosecutor and stating the date on which such evidence as aforesaid came to his knowledge shall be conclusive evidence of that fact; and a certificate stating that matter and purporting to be so signed shall be deemed to be so signed unless the contrary is proved.