(1)An assessment of a penalty under this Chapter in respect of any amount must be made on or before the later of date A and (where it applies) date B.
(2)Date A is the last day of the period of 2 years beginning with—
(a)in the case of failure to make a return, the filing date, or
(b)in the case of failure to pay tax, the last date on which payment may be made without paying a penalty.
(3)Date B is the last day of the period of 12 months beginning with—
(a)in the case of failure to make a return—
(i)the end of the appeal period for the assessment of the liability to tax which would have been shown in the return, or
(ii)if there is no such assessment, the date on which that liability is ascertained or it is ascertained that the liability is nil, or
(b)in the case of failure to pay tax—
(i)the end of the appeal period for the assessment of the amount of tax in respect of which the penalty is assessed, or
(ii)if there is no such assessment, the date on which that amount of tax is ascertained.
(4)In subsection (3)(a)(i) and (b)(i) “appeal period” means the period during which—
(a)an appeal could be brought, or
(b)an appeal that has been brought has not been determined or withdrawn.