57. In any proceedings for an offence consisting of a contravention of regulation 18 in relation to the packing of goods in metal—
(a)IBCs; or
(b)drums,
exceeding 50 litres in capacity, it shall be a defence for the person charged to prove that the IBCs or drums in question were manufactured less than 15 years prior to the date of consignment and prior to 1st July 1995.