Section 10 of the Principal Act is amended in subsection (4) -
(a) by substituting "for the purposes of paragraph (a) or (b) of section 5(3)" for "for the purposes of section 5(3)", and
(b) by inserting ", and the amount on which tax is chargeable in relation to a supply of services by virtue of regulations made for the purposes of section 5(3)(c) shall be the open market price of the services supplied" after "as the case may be".