27(1)References in this Schedule to " past relief", in relation to a trade carried on by any person in any period of account, are to the aggregate amount of the following reliefs allowed to him (or treated as allowed to him)—
(a)Schedule 10 relief (as defined in paragraph 18 of Schedule 5 to the [1976 c. 40.] Finance Act 1976) allowed for that trade;
(b)relief under Part I or Part II of that Schedule allowed for that trade; and
(c)relief under Part II or Part III of this Schedule in respect of earlier periods of account.
(2)Subject to sub-paragraphs (3) to (5) below and to paragraphs 4(3), 14, 15 and 20(3) above, the amount of unrecovered past relief in any period of account is that aggregate amount less the aggregate of the amounts on which charges by way of recovery of relief (whether under this Schedule, Schedule 5 to the said Act of 1976 or paragraph 8 of Schedule 7 to the [1980 c. 48.] Finance Act 1980) have been made on that person for that trade in respect of earlier periods of account.
(3)There shall be excluded from the amount of unrecovered past relief in any period of account so much of that amount (if any) as is attributable to relief allowed under Part I or Part II of Schedule 5 to the said Act of 1976 or under Part II or Part III of this Schedule in respect of any period of account which ended six years or more before the beginning of the first-mentioned period.
(4)There shall be excluded from the amount of unrecovered past relief in any period of account beginning after—
(a)the end of the period or the last period of account ending in the financial year 1978 (in the case of a company) or the year 1978-79 (in other cases); or
(b)if there is no such period of account, the end of the period of account current at the end of that financial year or year of assessment, as the case may be,
so much of that amount (if any) as is attributable to Schedule 10 relief.
(5)For the purpose of attributing the amount of unrecovered past relief in any period to Schedule 10 relief, to relief allowed under Part I or Part II of Schedule 5 to the said Act of 1976 or to relief allowed under Part II or III of this Schedule in respect of any previous period it shall be assumed that relief is recovered from later periods before earlier periods.