# Finance Act 2021, Paragraph 18


(1) An assessment of a penalty under this Schedule 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 the date specified in or for the purposes of column 3 of the relevant table in paragraph 1 ....
(3) Date B is the last day of the period of 12 months beginning with—
(a) the end of the appeal period for the assessment of the amount of tax in respect of which the penalty is assessed, or
(b) if there is no such assessment, the date on which that amount of tax is ascertained.
(4) In sub-paragraph (3)(a) “appeal period” means the period during which—
(a) an appeal could be brought (ignoring any possibility of an appeal out of time), or
(b) an appeal that has been brought has not been determined or withdrawn.

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Source: https://www.legislation.gov.uk/ukpga/2021/26/schedule/26/paragraph/18 (the official version)
Page: https://openlegislation.uk/finance-act-2021/schedule-26/paragraph-18
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.