Beta This part of GOV.UK is being rebuilt – find out what this means

HMRC internal manual

Tax Credits Technical Manual

HM Revenue & Customs
, see all updates

Decision Making: Valid Claims, Conclusive Entitlement and Changes to Decisions: Changes to a conclusive decision


If a conclusive decision has been made and none of the parts of the Tax Credits Act or the Taxes Management Act detailed below allow a revision, then the decision must stand and cannot be altered, even if it is incorrect. To alter this decision would be unlawful.

Please see the glossary at TCTM09530 for a definition of conclusive decision.

There are different parts of the Tax Credits Act that allow changes to an earlier conclusive decision, but only at specific times of the year and in prescribed circumstances.

Section 18 (for full detail see TCTM06106) - says that a conclusive decision can be revised if the claimant makes a new declaration or statement before 1SD (or 2SD if they supplied estimated income by 1SD).

When a claimant has provided a declaration or statement of estimated income an initial decision on entitlement under s18(1) is made. A second decision on entitlement, this time under s18(6) is made if the claimant provides actual income by 2SD or after 2SD where they do not. Where the claimant does not provide their actual income, HMRC make the second decision treating the estimate as their actual for the year. Both of these decisions carry the right of appeal as outlined in s38(1)(b) of the Tax Credits Act.

Section 19 - allows an enquiry to be opened as long as certain criteria are met (for full detail see TCTM09410). If the findings of this enquiry are that something is wrong with the claim, then the original decision can be revised.

Note: time limits on opening an enquiry are detailed at TCTM09410

Section 20 (for full detail see TCTM09420) - allows a decision to be revised where the board has reasonable grounds for believing that a conclusive decision relating to entitlement is not correct. There are various specific criteria that apply to this and s20 can be applied in two circumstances:  

  • where the claimant’s income tax liability has changed (the full list of applicable changes is at s20 TCA, TCTM12000)
  • where the board reasonably believe that the incorrect decision is attributable to fraud or neglect attributable to the claimant(s)

The time limits for a s20 decision are at TCTM09420

Section 21 (for full detail see TCTM09430) - allows a decision to be revised if it is incorrect due to ‘official error’ and:  

  • the new decision is in the claimant’s favour, and
  • the claimant did not materially contribute to the error (Official Error Regulations 2003)

Note: A decision made using s21 may only be revised at any time not later than five years after the date of the decision. (Prior to 6 April 2010 this read as five years after the end of the tax year to which the decision relates).


If a claimant appeals against a conclusive decision, the appeal is successful and a tribunal directs HMRC to amend a decision, this can (and should) be done.

In addition, HMRC on receipt of an appeal can choose to revise a decision under s54 of the Taxes Management Act 1970. This allows HMRC to settle an appeal on the basis that the appeal would be successful if it were to go to tribunal (full detail of this can be found in the Taxes Management Act s54).