`(1) The total tax payable by a participator in an oil field for the chargeable period or periods comprised in any calendar year shall not exceed 80 per cent. of the amount (if any) by which his adjusted profit for that year (as defined in this section) exceeds 30 per cent. of his accumulated capital expenditure at the end of that year (as so defined).
(2) For a participator in an oil field, his adjusted profit (if any) for any calendar year shall be determined as follows—
( a) for each chargeable period comprised in that year there shall be ascertained—
( b) in the case of each such chargeable period—
( c) if the year comprises only one chargeable period, his adjusted profit (if any) for that period is his adjusted profit for the year;
( d) if the year comprises two chargeable periods then—
(3) For a participator in an oil field his accumulated capital expenditure at the end of any calendar year is the total amount of expenditure taken into account under section 2(9)( b)(i) and ( c)(i) of this Act in computing the assessable profit or allowable loss accruing to him in each of the relevant chargeable periods, that is to say the chargeable period or periods comprised in that year and all earlier chargeable periods, excluding all expenditure so taken into account which was not allowed as qualifying for supplement under section 2(9)( b) (ii) or ( c)(ii):
Provided that in the case of a participator who has made an election under paragraph 9 of Schedule 3 to this Act, his accumulated capital expenditure at the end of any calendar year shall be taken to be what it would have been if he had made no such election.
(4) Any reduction necessitated by this section in the total tax otherwise payable by a participator in an oil field in respect of a calendar year comprising two chargeable periods shall be made as far as possible by reducing or extinguishing the tax otherwise payable by him for the later of those periods.
(5) In the case of any oil field the preceding provisions of this section shall have effect as if the calendar year which comprises the critical half year as defined in section 1(4) of this Act comprised the whole of the first chargeable period '.— [ Mr. Dell.]