Sch 15 para 102
(1) The seller's “reference accounting period” is the accounting period which is, at the licence transfer date, the seller's most recent qualifying accounting period in respect of which the amendment period has ended. (2) The “ amendment period ”, in relation to an accounting period, is 12 months beginning with the filing date for the company tax return for the accounting period. (3) In this paragraph “ filing date ” has the same meaning as in Schedule 18 to FA 1998 (see paragraph 14 of that Schedule).