3(1)This paragraph applies in the case of any oil field from which oil began to be won in commercial quantities before 13th November 1974.
(2)Expenditure incurred before that date which, apart from this paragraph, would be allowable under section 3 or 4 of this Act for an oil field shall be so allowable only to the extent that it was incurred—
(a)in connection with that field for one or more of the purposes mentioned in paragraphs (a) to (c) of section 3(1) of this Act; or
(b)in acquiring, bringing into existence, or enhancing the value of an asset used on or after that date in connection with the field.