(1)  Unless this Act otherwise provides, proceedings for an offence may be commenced within –

(a) the period of 2 years after the commission of the alleged offence; or

(b) a further period of one year commencing on the day on which the Competent Authority or an authorised officer first obtained evidence of the commission of the alleged offence considered reasonably sufficient by the Authority or officer to warrant commencing proceedings.

(2)  For the purposes of subsection (1) , a certificate purporting to have been issued by the Competent Authority or an authorised officer as to the date when the Authority or the officer first obtained evidence considered reasonably sufficient by the Authority or officer to warrant commencing proceedings is admissible in any proceedings and is prima facie evidence of the matters stated.