7. After section 173 of the Principal Act the following section is inserted in Part X:
“173A. (1) In proceedings for an offence against this Part, a certificate signed by a drug inspector stating that at a specified time a specified substance was included in Schedule 1 to the regulations is evidence of the matters stated.
“(2) For the purposes of subsection (1), a certificate that purports to be signed by a drug inspector shall, unless the contrary is proved, be taken to have been so signed.”.