Sch. 25 para. 14 in force at 6.4.2024 for specified purposes by S.I. 2024/440, reg. 2(1)
An assessment of a penalty under this Schedule may not be made after the later of Date A and (where it applies) Date B.
Date A is the end of the period of 2 years beginning with the due date.
Date B is the last day of the period of 12 months beginning with—
the end of the appeal period for the assessment of the liability to tax which would have been shown in the return, or
if there is no such assessment, the date on which that liability is ascertained or it is ascertained that the liability is nil.
In sub-paragraph (3)(a) “
an appeal could be brought (ignoring any possibility of an appeal out of time), or
an appeal that has been brought has not been determined or withdrawn.
Sub-paragraph (1) does not apply to a re-assessment under paragraph 11(3).
A re-assessment under that paragraph must be made before the end of the period of 2 years beginning with the day on which the return is made.