45U.K.No discovery assessment for an accounting period for which the company has delivered a company tax return, or discovery determination, may be made if—
(a)the situation mentioned in paragraph 41(1) or (2) is attributable to a mistake in the return as to the basis on which the company’s liability ought to have been computed, and
(b)the return was in fact made on the basis or in accordance with the practice generally prevailing at the time when it was made.