(1) For the year 1980-81 and each subsequent year a levy, to be known as gas levy, shall be payable out of his revenues by any person in respect of gas to which this section applies and which is supplied to or won by that person in that year.
(2) This section applies—
(a) to gas purchased by any person under a tax-exempt contract; and
(b) to gas which is—
(i) won or purchased by any person ; and
(ii) derived from a tax-exempt reservoir under the authority of a petroleum production licence which is or was held by a person who had agreed to supply gas from that reservoir to the British Gas Corporation (in this section referred to as “the Corporation ”) under a tax-exempt contract or under the authority of a petroleum production licence substituted for such a licence.
(3) In this section—
“ petroleum production licence ” means a licence granted under section 2 of the Petroleum (Production) Act 1934, including a licence granted under that section as applied by section 1(3) of the Continental Shelf Act 1964;
“ tax-exempt contract ” means a contract made before the end of June 1975 for the sale to the Corporation of gas won under the authority of a petroleum production licence; and
“ tax-exempt reservoir ” means a natural reservoir, gas derived from which the Corporation was on 1st April 1980 obliged to purchase (whether immediately or at some future date) under terms comprised in a document which on 1st April 1980 was treated for the purposes of paragraph (a) of section 10(1) of the Oil Taxation Act 1975 as containing the whole or part of a contract for the sale of excluded oil as defined in that subsection.