12(1)Where a company carries on a trade in respect of which it is within the charge to corporation tax under Case I of Schedule D it shall, subject to the provisions of this Schedule, be entitled to relief under this paragraph in respect of a period of account if—
(a)there is an increase in the all stocks index over that period; and
(b)the value of its trading stock at the end of the preceding period of account exceeded £2,000.
(2)The relief shall be calculated by reference to the amount by which the value of the trading stock referred to in sub-paragraph (1)(b) above exceeded £2,000 and, subject to sub-paragraph (4) below, shall be equal to such percentage of that amount as corresponds to the percentage increase in the all stocks index over the period referred to in sub-paragraph (1)(a) above.
(3)A company shall not be entitled to relief under this paragraph unless a claim for the relief is made within two years after the end of the period of account in respect of which the relief is claimed.
(4)A company may, in making a claim for relief under this paragraph in respect of any period of account, specify an amount of relief less than that available under sub-paragraph (2) above and, if it does so, the relief to which it is entitled under this paragraph in respect of that period shall be the amount specified in the claim.