Can HMRC reopen an enquiry once it is closed

Q: How does this work in practice?

Illustration only. Priya, a self employed consultant, receives a final closure notice for her 2022 to 2023 return after an enquiry into her motor expenses. The notice makes a small amendment and she pays the extra tax. Two years later HMRC receives bank data showing a second business account she never mentioned, with income paid into it. HMRC cannot open a new enquiry into the 2022 to 2023 return, because section 9A(3) allows only one. HMRC can consider a discovery assessment. The officer could not reasonably have known about income in an account that was never disclosed, so the second condition is likely to be met, and leaving income out of a return may also be careless or deliberate. If, instead, Priya had given HMRC the second account's statements during the enquiry and the officer simply did not pick up the income, a later officer would find it much harder to rely on the second condition, and HMRC would need to show carelessness.

Q: Are there other ways a closed year can be revisited?

A few situations come up regularly: Partial closure notices. For the second condition, section 29(5)(b) measures awareness at the time of the partial closure notice on that matter, so an issue settled early has its information tested at that earlier date. Your own amendment. As above, amending a closed return gives HMRC a new, limited enquiry into the amendment. Companies being wound up. EM8260 allows an officer, in limited cases such as companies in liquidation, to confirm that HMRC does not propose to enquire into a return. Even then, the guidance says a discovery assessment remains possible if further information later comes to light. Information notices. Paragraph 21 of Schedule 36 to Finance Act 2008 stops HMRC issuing a taxpayer notice to check the income tax or corporation tax position for a period covered by a return unless an enquiry is open or another condition applies, one of which is that an officer has reason to suspect a loss of tax. See our page on the Schedule 36 information notice.

No. Once HMRC has issued a final closure notice, it cannot open a second enquiry into the same return unless you later amend that return, and even then the new enquiry is limited to the amendment. HMRC can still collect more tax for that year only by making a discovery assessment, and after an enquiry that is allowed only if the loss was caused carelessly or deliberately or if the officer could not reasonably have spotted it from the information you gave.

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What does it mean when HMRC closes an enquiry?

An enquiry into a personal or trustee return under section 9A of the Taxes Management Act 1970 (TMA 1970) ends when an officer issues a final closure notice under section 28A(1B). The notice must state the officer’s conclusions and either say that no amendment of the return is needed or make the amendments needed to give effect to those conclusions. Under section 28A(3) it takes effect when it is issued. HMRC can also close individual issues earlier with a partial closure notice under section 28A(1A); see partial closure notices.

If you disagree with the conclusions or amendments, section 31(1)(b) gives a right of appeal, and section 31A requires the notice of appeal to be in writing, to the officer who issued the closure notice, within 30 days of the date it was issued, stating the grounds. Our page on the HMRC closure notice covers that stage in more detail. This page deals with what happens afterwards.

Can HMRC open a second enquiry into the same return?

Not into the same return. Section 9A(3) TMA 1970 says a return which has been the subject of one notice of enquiry may not be the subject of another, except one given in consequence of an amendment of the return under section 9ZA. Paragraph 24(5) of Schedule 18 to Finance Act 1998 applies the same rule to company tax returns: one notice of enquiry per return, unless the company itself amends the return.

The amendment exception is narrow. Under section 9A(5), where a notice of enquiry is given because of an amendment made after a final closure notice has been issued, the new enquiry is limited to what the amendment relates to or affects. So a late amendment to claim a forgotten relief reopens that relief to scrutiny, but it does not give HMRC a second look at the whole return. If you are thinking about amending a return that has already been through an enquiry, read enquiries into amended returns first.

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So how can HMRC still collect more tax for a closed year?

Through a discovery assessment. Section 29(1) TMA 1970 allows an officer who discovers that income or gains have not been assessed, that an assessment is insufficient or that a relief is excessive to make an assessment to make good the loss of tax. The company equivalent is in paragraphs 41 to 45 of Schedule 18 to Finance Act 1998. A discovery assessment is a separate assessment, not a reopening of the enquiry, so the enquiry stays closed and the closure notice still stands.

HMRC’s Enquiry Manual at EM3231 says a discovery must be more than mere suspicion, but that there do not need to be any new facts. An officer can make a discovery by newly reaching the conclusion that tax has been lost, including by changing their opinion. EM3231 also records the Supreme Court’s decision in HMRC v Tooth [2021] UKSC 17 that there is no principle of collective knowledge within HMRC, so one officer’s knowledge is not treated as known to another. EM3260 adds that, following the same case, a discovery does not become stale with the passage of time.

Our guide to the HMRC discovery assessment explains the wider rules.

What protects a year that has already been through an enquiry?

Where you delivered a return for the year, section 29(3) says you cannot be assessed by discovery unless one of two conditions is met:

The first condition (section 29(4)) is that the loss of tax was brought about carelessly or deliberately by you or a person acting on your behalf.
The second condition (section 29(5)) is that, at the time the officer issued the final closure notice (or a partial closure notice on the matter in question), the officer could not have been reasonably expected, on the basis of the information made available before that time, to be aware of the loss of tax.

Section 29(6) defines information made available. It includes the return and accompanying accounts and documents, any claim for the year, documents and particulars you produced for the purposes of the enquiry, and information whose existence and relevance could reasonably be inferred from that material or that you notified to HMRC in writing. Section 29(7) widens “the return” to include your returns for the two preceding years. For companies, paragraph 44 of Schedule 18 uses the same structure, measured at the time of the final or relevant partial closure notice.

EM3233 describes this as a test of disclosure. It is not enough for the information to have made a hypothetical officer aware that they ought to ask questions; it must have been enough to make them aware of the actual insufficiency.

There is also a separate protection in section 29(2). If the return was made in accordance with the practice generally prevailing at the time, there can be no discovery assessment for an error about the basis of computation. EM3234 says such a practice must be relatively long established, readily ascertainable and accepted by HMRC, and that the burden of showing it is on the person who relies on it.

How long does HMRC have to make a discovery assessment?

The time limits run from the end of the tax year or accounting period, not from the closure notice.

Behaviour	Individuals (TMA 1970)	Companies (FA 1998 Sch 18 para 46)
Neither careless nor deliberate	4 years after the end of the tax year (section 34)	4 years after the end of the accounting period
Careless	6 years (section 36(1))	6 years
Deliberate, or failure to notify	20 years (section 36(1A))	20 years

In practice, after a closed enquiry, a 4 year assessment relies on the second condition, which is hard for HMRC to meet where the point was explored in the enquiry. Most assessments of closed years therefore depend on showing careless or deliberate behaviour, which also extends the time limit. Our page on how far back HMRC can go sets out the wider picture.

How does this work in practice?

Illustration only. Priya, a self employed consultant, receives a final closure notice for her 2022 to 2023 return after an enquiry into her motor expenses. The notice makes a small amendment and she pays the extra tax. Two years later HMRC receives bank data showing a second business account she never mentioned, with income paid into it.

HMRC cannot open a new enquiry into the 2022 to 2023 return, because section 9A(3) allows only one.
HMRC can consider a discovery assessment. The officer could not reasonably have known about income in an account that was never disclosed, so the second condition is likely to be met, and leaving income out of a return may also be careless or deliberate.
If, instead, Priya had given HMRC the second account’s statements during the enquiry and the officer simply did not pick up the income, a later officer would find it much harder to rely on the second condition, and HMRC would need to show carelessness.

Are there other ways a closed year can be revisited?

A few situations come up regularly:

Partial closure notices. For the second condition, section 29(5)(b) measures awareness at the time of the partial closure notice on that matter, so an issue settled early has its information tested at that earlier date.
Your own amendment. As above, amending a closed return gives HMRC a new, limited enquiry into the amendment.
Companies being wound up. EM8260 allows an officer, in limited cases such as companies in liquidation, to confirm that HMRC does not propose to enquire into a return. Even then, the guidance says a discovery assessment remains possible if further information later comes to light.
Information notices. Paragraph 21 of Schedule 36 to Finance Act 2008 stops HMRC issuing a taxpayer notice to check the income tax or corporation tax position for a period covered by a return unless an enquiry is open or another condition applies, one of which is that an officer has reason to suspect a loss of tax. See our page on the Schedule 36 information notice.

What should you do if HMRC raises a closed year again?

Ask the officer which statutory route they are relying on; the legislation does not allow an enquiry to be reopened. If HMRC issues a discovery assessment, section 31(1)(d) gives a right of appeal and section 31A requires it within 30 days of the notice of assessment. Section 29(8) says an objection that neither condition is met can only be made on an appeal against the assessment, so the time limit for appealing is critical.

Common mistakes include:

assuming a closure notice gives complete immunity for the year, when deliberate or careless errors can still be assessed for up to 20 or 6 years;
relying on things said in a phone call or meeting rather than written notification, when section 29(6)(d)(ii) refers to information notified in writing;
missing the 30 day appeal deadline and losing the chance to argue that the discovery conditions were not met.

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Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 24 October 2026. Part of Accountapedia, the Solar Protect guide to UK tax and accounting. This page is general information, not personalised advice.