122Charge of supplementary petroleum duty
(1)Every participator in an oil field shall, in accordance with this Part of this Act, be chargeable with a tax (to be known as supplementary petroleum duty) on the gross profit accruing to him from the field in any chargeable period to which this section applies.
(2)The duty shall be charged at the rate of 20 per cent.
(3)For the purposes of the duty the gross profit shall, except so far as otherwise provided in this Part of this Act, be determined in accordance with section 2(4) and (5) of the [1975 c. 22.] Oil Taxation Act 1975 (" the principal Act") as for the purposes of petroleum revenue tax.
(4)Any other expression used in this Part of this Act which also occurs in Part I of the principal Act shall be construed in the same way as for the purposes of that tax.
(5)This section applies to the chargeable periods ending on 30th June 1981, 31st December 1981 and 30th June 1982.