# Finance Act 2021, Paragraph 17


(1) A supplementary assessment may be made in respect of a penalty if an earlier assessment is based on an amount of tax due and payable that is found by HMRC to be an underestimate or insufficient.
(2) If an assessment in respect of a penalty is based on an amount of tax due or payable that is found by HMRC to be excessive, HMRC may by notice amend the assessment so that it is based upon the correct amount.
(3) An amendment under sub-paragraph (2)—
(a) does not affect when the penalty must be paid;
(b) may be made after the last day on which the assessment in question could have been made under paragraph 18.

---
Source: https://www.legislation.gov.uk/ukpga/2021/26/schedule/26/paragraph/17 (the official version)
Page: https://openlegislation.uk/finance-act-2021/schedule-26/paragraph-17
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.