Articles 17 and 27 of Sixth Council Directive 77/388/EEC, as amended by Council Directive 2004/7/EC of 20 January 2004, must be interpreted as not precluding a measure, such as that at issue in the main proceedings, authorised by Council Decision 89/534/EEC of 24 May 1989 authorising the United Kingdom to apply, in respect of certain supplies to unregistered resellers, a measure derogating from Article 11A(1)(a) of the Sixth Directive, pursuant to Article 27 of that directive, which derogates from Article 11A(1)(a) of that directive and under which the taxable amount for valued added tax (VAT) purposes of a direct sales company is the open market value of the goods sold at the stage of final consumption, where those goods are marketed through resellers not subject to VAT, even if that derogating measure does not take account, in one way or another, of the input VAT relating to demonstration items purchased by those resellers from that company.