21(1)Where a company has before the year 1966-67 incurred a loss in a trade carried on by it, such part, if any, of that loss as but for this Act might have been carried forward to that year under section 342 of the Income Tax Act 1952 may be dealt with under section 58(1) or (7) of this Act as if it were a loss incurred by the company while within the charge to corporation tax in respect of the trade, but incurred in an accounting period ending at the time when the company in fact comes within the charge to tax in respect of the trade.
(2)This paragraph shall apply to any amount which by virtue of section 345 of the [1952 c. 10.] Income Tax Act 1952, or of paragraph 3 of Schedule 3 to the [1954 c. 44.] Finance Act 1954, might be dealt with under section 342 as a loss incurred by a company in a trade as if that amount were a loss so incurred ; but where section 345 applies by virtue of section 443(1)(b) of that Act to any amount of share interest or loan interest paid by a registered industrial and provident society, this sub-paragraph shall not have effect except in relation to so much of the said amount as represents share interest or loan interest paid before the society comes within the charge to corporation tax in respect of its trade.