The Commissioners may by regulations modify sections 19 and 20 and Schedules 6 and 7 for the purpose of providing (in place of the provision for the time being contained in those sections and Schedules) for the manner of determining for the purposes of this Act the value of—
(a)a supply of goods, or
(b)a transaction in pursuance of which goods are acquired from another member State,
in a case where the goods are supplied or acquired under a trading stamp scheme (within the meaning of the M1Trading Stamps Act 1964 or the M2Trading Stamps Act (Northern Ireland) 1965) or under any scheme of an equivalent description which is in operation in another member State.