8(1)A participator who has given notice of appeal under paragraph 7 above against an assessment charging him with any duty for a chargeable period may, if he delivered a return for that period as required by paragraph 2 of Schedule 2 to the principal Act, withhold, until the determination or abandonment of the appeal, so much of the duty charged in the assessment as is the smaller of—
(a)the amount of the duty so charged ; and
(b)duty on the difference between—
(i)the aggregate of the consideration received or receivable for oil as stated in the participator's return in pursuance of sub-paragraph (2) of the said paragraph 2 and, subject to sub-paragraph (2) below, the market value of oil so stated ; and
(ii)the aggregate of the corresponding consideration and value as included in the assessment.
(2)Subject to sub-paragraph (3) below, where the market value of all the oil for which a market value is stated in the participator's return is, as stated in that return, less than the value which is produced for that oil by applying to it the average price mentioned in sub-paragraph (4) below, sub-paragraph (1) above shall have effect as if, for the reference to the market value of oil as so stated, there were substituted a reference to the value which is so produced for that oil.
(3)The comparison of values and the substitution required by sub-paragraph (2) above shall, in the case of an appeal by a participator whose return relates both to gas and to other oil, be made separately for the gas and for the other oil.
(4)The average price referred to in sub-paragraph (2) above is the average price at which all oil included in the relevant returns as oil delivered in the period covered by the returns and disposed of in sales at arm's length was so disposed of.
(5)The relevant returns for the purposes of sub-paragraph (4) above are all the returns of all the participators in all oil fields which—
(a)were made for the chargeable period preceding that to which the appeal relates ; and
(b)were delivered before the end of the chargeable period t© which the appeal relates.
(6)Where in determining the gross profit accruing to a participator from a field in a chargeable period the aggregate of the amounts mentioned in section 2(5)(a), (b) and (c) of the principal Act falls to be increased under section 123 of this Act (whether as respects all oil or as respects a particular kind or kinds of oil) the difference mentioned in sub-paragraph (1)(b) above (or, as the case may be, the difference so far as relating to oil of the particular kind or kinds in question) shall be increased by multiplying it by the fraction mentioned in subsection (2) of that section.