7(1)Every company tax return for an accounting period must include an assessment (a “self-assessment”) of the amount of tax which is payable by the company for that period—
(a)on the basis of the information contained in the return, and
(b)taking into account any relief or allowance for which a claim is included in the return or which is required to be given in relation to that accounting period.
(2)For this purpose a company tax return is regarded as a return for an accounting period if the period is treated in the return as an accounting period and is not longer than twelve months, even though it is not, or may not be, an accounting period.