11(1)Subject to the following provisions of this paragraph, where—U.K.
(a)there is a supply of goods or services; and
(b)any sum relevant for determining the value of the supply is expressed in a currency other than sterling,
then, for the purpose of valuing the supply, that sum is to be converted into sterling at the market rate which, on the relevant day, would apply in the United Kingdom to a purchase with sterling by the person to whom they are supplied of that sum in the currency in question.
(2)Where the Commissioners have published a notice which, for the purposes of this paragraph, specifies—
(a)rates of exchange; or
(b)methods of determining rates of exchange,
a rate specified in or determined in accordance with the notice, as for the time being in force, shall apply (instead of the rate for which sub-paragraph (1) above provides) in the case of any supply by a person who opts, in such manner as may be allowed by the Commissioners, for the use of that rate in relation to that supply.
(3)An option for the purposes of sub-paragraph (2) above for the use of a particular rate or method of determining a rate—
(a)shall not be exercised by any person except in relation to all such supplies by him as are of a particular description or after a particular date; and
(b)shall not be withdrawn or varied except with the consent of the Commissioners and in such manner as they may require.
(4)In specifying a method of determining a rate of exchange a notice published by the Commissioners under sub-paragraph (2) above may allow a person to apply to the Commissioners for the use, for the purpose of valuing some or all of his supplies, of a rate of exchange which is different from any which would otherwise apply.
(5)On an application made in accordance with provision contained in a notice under sub-paragraph (4) above, the Commissioners may authorise the use with respect to the applicant of such a rate of exchange, in such circumstances, in relation to such supplies and subject to such conditions as they think fit.
(6)A notice published by the Commissioners for the purposes of this paragraph may be withdrawn or varied by a subsequent notice published by the Commissioners.
(7)The time by reference to which the appropriate rate of exchange is to be determined for the purpose of valuing any supply is the time when the supply takes place; and, accordingly, the day on which it takes place is the relevant day for the purposes of sub-paragraph (1) above.