A practical guide to compliance checks, enquiries, penalties, and how to protect yourself.
An HMRC tax investigation means a civil compliance intervention where HMRC checks that the right amount of tax has been paid and that returns, claims and supporting records are accurate. HMRC generally refers to these as compliance checks. In UK, Self-Assessment, HMRC may also open a formal enquiry into a return within the statutory enquiry window. Most UK cases are resolved through civil processes, but where HMRC suspects fraud, the case can escalate into specialist fraud procedures.
This guide explains in the UK for 2025/26 how checks are triggered, what HMRC can ask for, how far back HMRC can go, the main penalty regimes, and the practical steps that help keep you safe.
It is general information, not a substitute for tailored advice on your circumstances.
What HMRC means by ‘compliance check’ and ‘enquiry’
A compliance check is HMRC’s umbrella term for reviewing a taxpayer’s position. The format varies by tax and by risk. For Self-Assessment, HMRC can open a formal enquiry into a tax return. For VAT and PAYE, HMRC may carry out assurance work, targeted reviews or visits. For companies, HMRC may open a Corporation Tax enquiry into a Company Tax Return.
When and Why HMRC opens a check
HMRC opens checks on a risk basis. Some are random, but most are prompted by risk signals from HMRC’s data, comparisons, or third-party information.
A check can start narrowly (one issue or one period) and expand if HMRC identifies wider risks. A good early response is to clarify scope, provide a tidy evidence pack, and keep communications controlled.
What the process looks like
Most checks are handled by correspondence and follow-up questions. HMRC may communicate by letter, phone and, increasingly, through digital channels. Where it helps HMRC understand your records and systems, a visit or meeting may be arranged.
Sample of Opening letter
Types of HMRC checks you should recognise
Common investigation formats include:
What HMRC can request (and the limits)
HMRC has statutory information powers. In many cases, HMRC requests information informally first. Where necessary, HMRC can issue an information notice requiring a taxpayer (or, in defined circumstances, a third party) to provide information or produce documents. The key limiter is that the information or document must be reasonably required to check the tax position.
Remember
Keep responses factual, indexed and complete. If a request feels too wide, address it promptly by asking HMRC to explain how the item is relevant and by proposing a narrower set that still meets the check objective
Records and evidence: how to support your return
HMRC will expect a clear audit trail from the tax return back to source evidence. Strong evidence is usually created at the time of the transaction and can be independently verified.
Where records are missing or incomplete, HMRC may accept reconstructed evidence, but the risk of estimates, challenge and penalties increases. If estimates are unavoidable, label them clearly, explain the method and assumptions, and update the figures when better information becomes available.
How far back HMRC can go: enquiry windows and assessment time limits
Time limits are an important protection and a common dispute point. Different taxes have different rules, and the applicable time limit often depends on behaviour (reasonable care, careless, or deliberate). HMRC may also use ‘discovery’ assessments where statutory conditions are met and the assessment is in time.
To put simply, HMRC must have identified that tax has been underpaid and, where a tax return has already been filed, must generally show either that the underpayment was caused by careless or deliberate behaviour, or that an HMRC officer could not reasonably have been expected to spot the issue from the information already available at the time (the “officer awareness” test). Cases have also raised “staleness” arguments, meaning HMRC waited too long after making the discovery, although HMRC’s published position is that staleness does not invalidate an otherwise in-time discovery assessment.
For Self Assessment, HMRC can normally open an enquiry within the enquiry window after the return is filed. Broadly, this is up to 12 months after the statutory filing date (or, if later, 12 months after the return is delivered). If you amend a return, that can affect the position: where the normal enquiry window is still open, HMRC can enquire into the return (including the amendment) in the usual way, but where the normal window has already closed, a valid amendment can give HMRC a further opportunity to open an enquiry, typically focusing on the amendment and anything that flows from it. If HMRC seeks to assess older periods, the analysis often turns on what information was made available to HMRC at the relevant time and whether the statutory conditions for assessment are met.
Tax Implications to the Freeholder
Tax
Normal time limit
Careless Behaviour
Deliberate behaviour
Notes
Income Tax and Capital Gains Tax | 4 years | 6 years | 20 years | A longer 12-year limit can apply for certain offshore matters. |
Corporation Tax | 4 years | 6 years | 20 years | Separate rules apply for enquiry windows and for cases where a return is not delivered. |
VAT (assessments) | Up to 4 years | Up to 4 years (plus other rules) | Up to 20 years in certain cases | Four years is the general maximum under VAT assessment powers, except where the statutory 20-year rule applies. Timing can also depend on when HMRC has evidence of facts sufficient to justify an assessment. |
Here, Careless behaviour means a tax return or claim is wrong because the person did not take reasonable care, for example they failed to keep proper records, did not check figures before filing, or made a claim without taking sensible steps to confirm the correct tax treatment when it was unclear.
Deliberate behaviour means the return or claim is wrong on purpose, in the sense that the person knew a figure or tax treatment was incorrect (or knew something should have been declared) but chose to submit it that way anyway, for example leaving out known income, inflating expenses, or claiming reliefs they know they are not entitled to. If they also take steps to hide it, such as creating or providing false invoices or altering records, HMRC may treat it as deliberate and concealed.
What is “Offshore matter”?
An offshore matter is where the tax issue is connected to something outside the UK, for example income arising overseas (such as foreign rental income or interest on an overseas bank account), or assets held abroad (such as overseas property or investments).
Is “Offshore Matter” and “Offshore Transfer” same?
An offshore transfer is slightly different: it is where the income or sale proceeds may have arisen in the UK, but they were paid into, moved to, or received in an overseas account or overseas location, so the money (or assets representing it) ends up offshore. These bring the 12-year assessment time limit into play for Income Tax and Capital Gains Tax in certain cases, even though the standard limits are usually 6 years in case of Careless behviour.
HMRC tax investigation penalties, interest and outcomes
If HMRC concludes that tax has been underpaid or a repayment has been overclaimed, it may charge additional tax and statutory interest. Penalties depend on the type of failure, behaviour, and the quality and timing of disclosure. Identifying the correct penalty regime early is essential.
Penalty map: which situation uses which regime
Situation HMRC identifies
Typical penalty regime
What HMRC looks at
Wrong figures/claims in a return or document (tax understated or repayment overstated) | Inaccuracy penalties (Schedule 24 Finance Act 2007) | Behaviour (careless or deliberate), prompted vs unprompted disclosure, quality of disclosure |
Tax was due but the person did not notify chargeability or register when required | Failure to notify (Schedule 41 Finance Act 2008) | Behaviour, timing of disclosure, reasonable excuse; different minimums may apply |
Return filed late (for example Self Assessment) | Late filing penalties (for example Schedule 55 Finance Act 2009) | How late; daily penalties; reasonable excuse |
Tax paid late (for example Self Assessment) | Late payment penalties (for example Schedule 56 Finance Act 2009) | How late; whether a Time to Pay arrangement exists; reasonable excuse |
Records incomplete or inadequate systems | Record-keeping failures can drive estimates and can support penalties in other regimes | Whether records meet statutory requirements; remedial actions and controls |
Penalty map: which situation uses which regime
Behaviour
Unprompted disclosure
Prompted disclosure
Careless | 0% to 30% | 15% to 30% |
Deliberate (not concealed) | 20% to 70% | 35% to 70% |
Deliberate and concealed | 30% to 100% | 50% to 100% |
Unprompted Disclosure
Telling HMRC about an inaccuracy, underpayment, or overclaimed repayment before HMRC has contacted you about checking that specific issue, tax, or period.
Prompted Disclosure
Disclosing the issue after HMRC has started a compliance check or enquiry or has contacted you in a way that makes it reasonable to think they are looking at your position (even if they have not yet identified the exact error).
Note
Higher ranges can apply for certain offshore inaccuracies. Where behaviour is careless, HMRC may suspend all or part of a penalty if practical conditions can be set that would help prevent a repeat careless inaccuracy. Suspension is not available for deliberate behaviour.
Self Assessment late filing and late payment: Penalties
In the UK Self Assessment system, HMRC charges penalties separately for late filing of the tax return and late payment of the tax due. Late filing penalties are triggered automatically once the filing deadline is missed, even if there is no tax to pay, and they increase the longer the return remains outstanding. Late payment penalties and interest apply if the tax is not paid by the due date, and these build over time based on how late the payment is and how much remains unpaid.
The table below summarises the main penalty points and time thresholds, but the exact position can vary in certain cases, such as where a taxpayer has a reasonable excuse or where the outstanding balance is later corrected.
Late filing (Self Assessment)
Penalty
1 day late | £100 |
3 months late | £10 per day (up to £900) |
6 months late | 5% of tax due or £300 (whichever is higher) |
12 months late | An additional 5% of tax due or £300 (whichever is higher) |
30 days late | 5% of unpaid tax |
6 months late | Additional 5% of unpaid tax |
12 months late | Additional 5% of unpaid tax |
Interest runs separately on late paid tax. If cash flow is an issue, it is usually better to engage early with HMRC about Time to Pay rather than wait for enforcement or penalty escalation.
How to deal with HMRC during an investigation:
Early actions (first week)
- 1Read the opening letter carefully and confirm the tax head and periods in scope.
- 2Preserve records immediately. Do not delete or overwrite accounting, payroll or bank data.
- 3Build an indexed evidence pack: bank statements, sales records, purchase invoices, payroll records, VAT account and workings (where relevant), contracts and key schedules.
- 4Reconcile return figures to source records and prepare short explanations for differences.
- 5Keep communications controlled: one point of contact, agreed deadlines, and a written log of what has been provided.
- 6Map the issue to the correct penalty regime early and assess behaviour and disclosure position before responding on penalty points.
What HMRC typically asks for (Common Request Lists)
Managing the scope of information requests
HMRC often starts with broad requests. A professional response is to agree scope and sequencing, provide a clear index and explanations, and ask HMRC to confirm what it needs next. Where a request appears over-broad, the key question is whether the item is reasonably required to check the tax position. Narrowing scope early can materially reduce cost and time.
Behaviour, disclosure quality and penalty mitigation
Penalties are driven by behaviour (careless vs deliberate) and reduced by quality of disclosure.
Mitigation is maximised by:
Disputes: Reviews, Appeals and Alternative Dispute Resolution (ADR)
If you disagree with HMRC’s conclusions, you may have rights to request an internal review and/or appeal to the First-tier Tribunal, depending on the decision. Alternative Dispute Resolution (ADR) can be effective where the dispute is fact-heavy or where both sides need a structured process to narrow issues.
Escalation risks: fraud procedures, serious defaulters and publication
Most checks remain civil. However, where HMRC alleges deliberate behaviour, the risk profile changes and early specialist input is critical.
COP9 and the Contractual Disclosure Facility (CDF)
Where HMRC suspects tax fraud, it may issue Code of Practice 9 (COP9) and offer the Contractual Disclosure Facility as a civil route. You normally have 60 days to accept or reject the offer.
Case 1 : IF CDF is Accepted
Case 2. IF CDF is Rejected
In brief , accepting COP9/CDF means you enter a civil disclosure agreement: you admit deliberate behaviour and commit to a complete, accurate disclosure, and HMRC agrees not to open a criminal investigation into the deliberate behaviour you disclose.
Managing Serious Defaulters (MSD)
If HMRC concludes that deliberate behaviour has occurred, it may consider the Managing Serious Defaulters programme. This can lead to enhanced monitoring and further compliance interventions.
Publishing details of deliberate defaulters
HMRC may publish details of deliberate defaulters where conditions are met. Publication is separate from the tax and penalty itself. It generally requires that deliberate penalties have been incurred and that the potential lost revenue exceeds a statutory threshold (commonly more than £25,000).
Record retention: what to keep and for how long
Record retention is central because HMRC investigations are evidence-led. Keep records longer where a compliance check is open or where the same documents support multiple taxes with different retention periods.
Staying safe: steps that reduce investigation risk
The best defence in an HMRC check is a clean audit trail and consistent controls. These steps materially reduce risk and cost:
How UKPA can help
An HMRC investigation is manageable with the right approach, but it can quickly become expensive and stressful if scope expands or behaviour is challenged. UKPA can support individuals and businesses through every stage of the process, including:
If you have received a letter from HMRC, or you are concerned about a potential issue, contact UKPA early. Early advice helps contain scope, protect your position, and minimise penalties
Disclaimer
This article provides general information and does not constitute tax or legal advice. Tax outcomes depend on the specific facts and the law in force at the time.
Other FAQs
Yes, but it can be risky if the issues are technical or the information request is wide. It is easy to miss deadlines, provide inconsistent explanations, or share more than HMRC is entitled to ask for, which can increase the scope, penalties or time it takes to resolve. In many cases, having an experienced adviser involved helps keep communications focused and protects your position.
It depends on the complexity of the issues, how quickly information is provided, and whether HMRC accepts the explanation. Straightforward checks can conclude relatively quickly once HMRC has what it needs, but complex or disputed cases can run for many months.
Do not ignore it. Check the deadline in the letter, gather the documents requested, and consider appointing an agent immediately if the issues are technical or the request is wide.
If you ignore an HMRC letter, the matter usually escalates. HMRC may issue a formal information notice (with penalties for non-compliance) and can raise an assessment using the information they hold which can be harder and more costly to challenge later. You can also miss strict deadlines for reviews or appeals.
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