UK HMRC Tax Investigation Guide (2026/27)

1. Overview: the HMRC investigation landscape

HMRC investigates several hundred thousand tax positions every year across Self Assessment, PAYE, VAT, Corporation Tax and indirect tax regimes. The popular shorthand "tax investigation" covers a spectrum: a single-item aspect enquiry that resolves within months on one side, a multi-year fraud investigation under Code of Practice 9 leading to prosecution on the other. The legal framework is principally the Taxes Management Act 1970 (Section 9A enquiry powers, Section 28A closure notices, Section 29 discovery assessments), Finance Act 2007 Schedule 24 (inaccuracy penalties), Finance Act 2008 Schedule 36 (information powers and notices) and the published HMRC Enquiry Manual.

Who gets investigated is partly random and overwhelmingly risk-based. A small fraction of Self Assessment returns are selected for random enquiry each year - the exact rate is not published but historically estimated under 1% of returns - to validate compliance levels across the population. The vast majority of enquiries are risk-targeted. HMRC's Connect database cross-references over 30 sources including Land Registry, DVLA, bank reporting under the Common Reporting Standard, eBay / Vinted / Airbnb / payment-processor data, credit reference files, foreign tax authority exchanges and social media. Any mismatch between the lifestyle and assets visible in those datasets and the income declared on the return triggers a risk score that may justify an enquiry.

The scale of HMRC compliance activity is substantial. HMRC's most recent annual report disclosed around £41 billion of compliance yield (the additional tax recovered through investigations and other compliance work) on a budget of roughly £4 billion - a ratio that explains why enquiry activity has grown each year despite political pressure to keep administrative costs down. The guide that follows is designed to help taxpayers and small-business owners understand the framework, recognise the rights they hold during an enquiry, and plan a measured response if a brown envelope arrives. Figures retrieved on 2026-05-23.

2. Types of enquiry

HMRC has multiple statutory routes to open a tax investigation. The label matters because it determines the scope, the powers HMRC will deploy and the appropriate defensive response.

Aspect enquiry

An aspect enquiry is the narrowest form: HMRC opens an enquiry under Section 9A Taxes Management Act 1970 but limits it to a single area of the return. Typical examples: a specific expense claim that appears disproportionate to declared turnover, an identifiable rental property where HMRC cross-references DVLA or Land Registry data, a one-off capital gain where the computation is contested, or a particular employment expenses claim. The opening letter usually narrows the scope expressly ("we want to look at your property income"). Aspect enquiries typically resolve within 3 to 6 months and result in either no change, a small amendment, or a Schedule 24 penalty calculated against the additional tax for that single item.

Full enquiry

A full enquiry reviews the entire Self Assessment return for the year in question. HMRC may follow the trail wherever the records take them, asking for source documents on every line item: P60 / P11D, bank statements, dividend vouchers, sale contracts, rental agreements, expense receipts, mileage logs. Full enquiries are more common where HMRC has flagged a lifestyle / declared-income mismatch or where multiple risk factors combine. They typically run 9 to 18 months and can produce material amendments across several heads of income. Full enquiries also frequently broaden into multi-year reviews if HMRC discovers patterns suggesting the original year was not isolated - this is where Section 29 discovery assessments enable HMRC to reach back into earlier closed years.

Random enquiry

A small proportion of Self Assessment returns are selected for random enquiry each year to validate compliance baselines across the taxpayer population. Random enquiries use the same Section 9A power as risk-based enquiries; the taxpayer cannot tell from the opening letter whether their case is random or targeted (HMRC does not disclose the trigger). In practice random enquiries are sometimes inferable from the breadth of the opening request and the absence of focus on a particular item, but this is rarely confirmed by HMRC. The penalty consequences are no different: random selection is not a mitigating factor.

Code of Practice 8 (COP8)

COP8 is the framework HMRC use where they suspect serious tax avoidance involving complex structures or planning arrangements but no criminal fraud. Typical examples include disguised remuneration schemes, EBT loan arrangements, contractor loan schemes, complex offshore structures and aggressive partnership planning. COP8 cases are usually run by the Fraud Investigation Service or specialist counter-avoidance teams. The investigation is civil and the outcome is typically settlement with full tax, interest and penalties under Schedule 24 (often at the deliberate band). COP8 investigations can run 18 to 36 months and almost always require specialist tax adviser representation.

Code of Practice 9 (COP9) and the Contractual Disclosure Facility

COP9 is HMRC's most serious civil procedure: the Contractual Disclosure Facility (CDF) for cases of suspected deliberate tax fraud. The taxpayer receives a hand-delivered or named-officer letter offering 60 days to admit deliberate conduct and produce an Outline Disclosure of the irregularities. In exchange for full and timely disclosure, HMRC undertakes not to pursue criminal prosecution for the disclosed conduct. The offer is a one-shot opportunity - declining COP9 or being later found to have concealed further fraud within an accepted COP9 preserves HMRC's right to refer the case for prosecution by the Crown Prosecution Service. Specialist tax investigations representation is essentially mandatory. Penalties under Schedule 24 typically apply at the deliberate-and-concealed band (50% to 100% of PLR for prompted offshore matters under Schedule 24A).

3. Time limits and Section 29 discovery

Two different time clocks apply. The first is the window for HMRC to open an enquiry into a return already filed. The second is the longer-tail window during which HMRC can issue a discovery assessment under Section 29 Taxes Management Act 1970 reaching into years for which the enquiry window has closed.

Window to open an enquiry (Section 9A)

For a Self Assessment return filed on time, HMRC has 12 months from the filing date to open an enquiry under Section 9A. For example, a 2024/25 return filed online on 15 January 2026 falls out of enquiry window on 15 January 2027. For a late-filed return, the window is 12 months from the end of the quarter in which the return was filed. Once the enquiry window closes, HMRC cannot reopen the return through a Section 9A enquiry - but the Section 29 discovery route remains available.

Discovery assessments (Section 29)

Section 29 Taxes Management Act 1970 enables HMRC to make a discovery assessment outside the enquiry window where they discover that an assessment to tax is insufficient and (broadly) the under-assessment was either not adequately disclosed in the return or was the result of careless or deliberate behaviour. The leading authority on what "adequate disclosure" means is HMRC v Tooth [2021] UKSC 17, which clarified that careless or deliberate inaccuracies are the gateway to discovery assessments where the return otherwise contained the relevant facts. The time limits are set by Section 34 to 36 TMA 1970:

The clock runs from the end of the tax year being assessed (5 April), not from the year the return was filed or the year HMRC discovered the issue. For 2024/25 (year ending 5 April 2025), a 4-year discovery assessment can be issued up to 5 April 2029, a 6-year assessment to 5 April 2031 and a 20-year deliberate assessment to 5 April 2045. HMRC bears the burden of proving careless or deliberate behaviour to access the longer windows (Section 36 TMA 1970). The taxpayer can appeal a discovery assessment to the First-tier Tribunal challenging both the substantive tax and HMRC's ability to invoke the longer time limit at all.

Offshore matters carry separate enhanced rules under Schedule 7 Finance Act 2019, including the 12-year window for non-deliberate offshore inaccuracies and the Requirement to Correct deadline that closed on 30 September 2018 with extended Failure to Correct penalties of 100% to 200% of PLR. Anyone with historical offshore exposure should take specialist advice before responding to any HMRC enquiry touching offshore matters. Retrieved 2026-05-23.

4. The enquiry process step by step

Self Assessment enquiries follow a structured procedural path set out across Sections 9A, 19A and 28A TMA 1970 and Schedule 36 FA 2008. Understanding each stage helps you respond proportionately and preserve your rights.

Stage 1: Notice of enquiry

HMRC issues a Section 9A enquiry notice citing the tax year and identifying the officer in charge. The notice does not need to explain the trigger or scope, though some HMRC offices include a narrowing letter ("we want to look at property income"). Once the notice is issued the enquiry is formally open and the taxpayer cannot file an amended return for the year under enquiry without HMRC's consent.

Stage 2: Information requests (Schedule 36)

HMRC follows up with information requests. The first round is typically an informal letter listing documents and questions. If the informal request is not fully met, HMRC can escalate to a formal Schedule 36 information notice (see section 5 below) which carries statutory consequences for non-compliance. The taxpayer or their adviser should respond to information requests in writing, keep contemporaneous records of what was provided, and challenge any requests that exceed the proper scope of the enquiry.

Stage 3: Optional meeting

HMRC often requests a face-to-face meeting to discuss the enquiry. There is no statutory obligation to attend. Many advisers recommend declining the meeting or, if attending, doing so with the adviser present and on the explicit understanding that anything discussed will be confirmed in writing. The risk in informal meetings is that casual statements get recorded as evidence and may later be used against the taxpayer. For COP9 cases the opening meeting is part of the structured CDF process and is unavoidable, though it should always be attended with specialist representation.

Stage 4: Settlement negotiations

Once HMRC has formed a view, they typically propose a settlement covering the additional tax, interest at base rate plus 2.5% from the original due date, and Schedule 24 penalties calibrated against the agreed behaviour band. The taxpayer can accept, partially accept (agreeing tax but contesting penalties) or reject the proposal. The negotiation phase is where specialist advisers add the most value, both on substantive tax positions and on Schedule 24 penalty mitigation through full cooperation, voluntary disclosure reductions and (for careless cases) suspended penalty terms.

Stage 5: Closure notice

The enquiry concludes with a closure notice under Section 28A TMA 1970. The notice states either that no amendment is required, or sets out the amendments HMRC propose. The taxpayer has 30 days from the closure notice to appeal in writing. If no appeal is lodged, the closure notice becomes final and the assessed tax becomes due. The taxpayer can also apply to the First-tier Tribunal under Section 28A(4) for a direction requiring HMRC to issue a closure notice if HMRC is dragging the enquiry on without reasonable cause - a powerful lever where the enquiry has stalled for over 12 months without substantive progress.

Stage 6: Statutory review and Tribunal appeals

An appealed closure notice can be referred to free internal statutory review (request within 30 days) followed by the First-tier Tribunal (Tax Chamber). The review process and tribunal mechanics are set out in section 8 below. Retrieved 2026-05-23.

5. Information notices under Schedule 36 FA 2008

Schedule 36 Finance Act 2008 is the statutory power HMRC use to compel production of documents and information during a tax investigation. The HMRC civil information powers page is the canonical reference; the CCFS10 factsheet sets out the penalty consequences for non-compliance.

What can HMRC demand?

An information notice can require the taxpayer (a "taxpayer notice" under paragraph 1 of Schedule 36) to produce documents or provide information that is reasonably required to check their tax position. The same power can also be used against third parties under paragraphs 2 and 3 (a "third party notice") - subject in those cases to approval from the First-tier Tribunal or written consent from the taxpayer. The "reasonably required" test is the legal limit: HMRC cannot use Schedule 36 to fish for information beyond what is genuinely necessary for the tax position being investigated. Documents protected by legal professional privilege are expressly excluded (paragraph 23).

Penalties for non-compliance

Failure to comply with a Schedule 36 notice triggers an initial £300 penalty under paragraph 39, escalating to £60 per day under paragraph 40 for continued failure. For sustained non-compliance HMRC can apply to the First-tier Tribunal under paragraph 50 for a tax-related penalty - effectively a percentage uplift tied to HMRC's best estimate of the tax at stake. Reasonable excuse (paragraph 45) applies as a statutory defence: genuine inability to access documents, third-party delay outside the taxpayer's control, or HMRC system failure on a critical date can all establish reasonable excuse if documented and remedied promptly.

Appealing a Schedule 36 notice

A taxpayer notice can be appealed to the First-tier Tribunal within 30 days under paragraph 29 (with the exception of notices issued with prior tribunal approval, which are not appealable). Common grounds for appeal: the requested documents are not reasonably required, the documents are protected by legal professional privilege, or the scope of the notice exceeds the proper boundaries of the enquiry. While the appeal is pending the notice is not enforceable and penalties cannot accrue. Retrieved 2026-05-23.

6. The penalty regime (Schedule 24 FA 2007)

Penalties for inaccuracies discovered during an enquiry are governed by Schedule 24 Finance Act 2007. The framework is behaviour-based and the percentage depends on whether the error was careless or deliberate, whether disclosure was prompted or unprompted, and the quality of cooperation with HMRC. See our dedicated HMRC penalties guide for the full detail; the table below summarises the bands you can expect in an investigation context.

The percentage is applied to the Potential Lost Revenue (PLR) - the additional tax that would have been understated had the enquiry not picked up the inaccuracy. Three disclosure reductions can move the rate within the band: telling (up to 30% of the available reduction for admitting the error and explaining how it happened), helping (up to 40% for quantifying the inaccuracy and supporting HMRC's quantification) and giving access (up to 30% for allowing HMRC to inspect records). Combined, full cooperation collapses the penalty to the floor of the band.

Schedule 24A (introduced by Finance Act 2015) raises the ceilings for offshore matters: penalties of up to 200% of PLR apply for category 3 territories where the relevant tax was lost as a result of deliberate behaviour. The Worldwide Disclosure Facility provides a structured route to access the unprompted-disclosure floor for offshore exposures (see section 7). HMRC's full reference is the inaccuracies in returns or documents publication. Schedule 41 (failure to notify chargeability), Schedule 55 (late filing) and Schedule 56 (late payment) run alongside Schedule 24 in any enquiry where the underlying conduct also engages those regimes.

For careless penalties only, HMRC has discretion under paragraph 14 of Schedule 24 to suspend the penalty for up to 24 months on conditions designed to prevent recurrence (eg switching to accounting software, having an accountant review future returns). Successfully meeting the conditions cancels the penalty entirely. Suspension is not available for deliberate or deliberate-and-concealed penalties. Retrieved 2026-05-23.

7. Disclosure facilities

HMRC operates several structured disclosure facilities that allow taxpayers to come forward voluntarily about unreported income or gains. The penalty consequences of unprompted disclosure are materially better than waiting to be caught: 0% floor on careless errors (vs 15% prompted), 20% floor on deliberate (vs 35% prompted), 30% floor on deliberate and concealed (vs 50% prompted).

Worldwide Disclosure Facility (WDF)

The Worldwide Disclosure Facility is the route for taxpayers with undeclared offshore income, assets or gains. Following the closure of the Liechtenstein Disclosure Facility and the Crown Dependencies disclosure facilities, the WDF is the standing channel. It requires full disclosure of all offshore matters, payment of tax plus interest, and Schedule 24 / 24A penalties calibrated against the behaviour. The WDF is technical and time-bound - specialist advice is strongly recommended before contacting HMRC, particularly given the Failure to Correct penalties under Schedule 18 Finance (No 2) Act 2017 (100% to 200% of PLR for offshore matters that should have been corrected by 30 September 2018).

Let Property Campaign

The Let Property Campaign is HMRC's standing disclosure channel for landlords with undeclared rental income. Targets include accidental landlords (former main residences let out during relocation), short-term let hosts (Airbnb, Booking.com) and traditional buy-to-let landlords who have not registered for Self Assessment. The campaign requires full disclosure of all undeclared rental income going back as far as the behaviour requires (4 years ordinary, 6 careless, 20 deliberate), payment of tax plus interest, and reduced penalties. The disclosure can be made through the Digital Disclosure Service portal on gov.uk. See our UK landlord tax guide for the underlying tax position.

Contractual Disclosure Facility (CDF / COP9)

The CDF is the disclosure side of Code of Practice 9 - the route for taxpayers who recognise they have committed deliberate tax fraud and wish to disclose it in exchange for HMRC's undertaking not to pursue criminal prosecution. The CDF can either be triggered by HMRC issuing a COP9 letter or by the taxpayer self-initiating a CDF application. The 60-day Outline Disclosure deadline, the structured Scoping Document process and the final settlement require specialist tax investigations representation. Acceptance of the CDF means HMRC will not prosecute for the disclosed conduct, but penalties at the deliberate-and-concealed band still apply.

Voluntary Disclosure (Digital Disclosure Service)

For ad-hoc unreported income that does not fit a named campaign (eg an unreported capital gain, a one-off freelance income source, an inherited asset that generated undeclared income) HMRC's Digital Disclosure Service allows a general voluntary disclosure. The same Schedule 24 unprompted-disclosure reductions apply, and the disclosure can be made online through gov.uk. Specialist advice is recommended where the amounts are material or where the unreported position spans multiple years. Retrieved 2026-05-23.

8. Closure notice and appeals

An enquiry concludes with a closure notice under Section 28A TMA 1970. From there a structured appeal route runs through statutory review, the First-tier Tribunal, the Upper Tribunal, and exceptionally to the Court of Appeal and Supreme Court.

Statutory review (free, 30 day deadline)

Request a statutory review within 30 days of the closure notice by writing to the address on the notice. A different HMRC officer who was not involved in the case reviews the decision and issues a conclusion within 45 days (extendable to 75 by mutual agreement). The review can uphold, vary or cancel the original decision. Statutory review costs nothing, does not prejudice the right to appeal further, and historically results in around 30% of decisions being varied or cancelled at this stage. The First-tier Tribunal clock restarts on the date of the review conclusion letter.

First-tier Tribunal (Tax Chamber)

Appeal to the First-tier Tribunal within 30 days of the closure notice (if you bypass statutory review) or within 30 days of the review conclusion. Use the T240 Notice of Appeal from HMCTS. The tribunal categorises appeals as default paper, basic, standard or complex - most aspect enquiry penalty disputes are default paper or basic, decided on documents alone or after a short telephone hearing. No tribunal fee applies to tax appeals. Typical timeline: 4 to 8 months for default paper, 8 to 12 months for basic, 12 to 24 months for standard or complex. The gov.uk tax appeals portal links the entire process end to end.

Upper Tribunal and onward

Appeal to the Upper Tribunal (Tax and Chancery Chamber) within 56 days of the FTT decision, on a point of law only. Errors of fact are not appealable. Permission must be granted by the FTT or, if refused, by the Upper Tribunal directly. Upper Tribunal hearings are public and formal; representation by counsel is usual though not mandatory. Beyond the Upper Tribunal, permission to appeal to the Court of Appeal and ultimately the Supreme Court is rare and reserved for genuinely novel points of UK tax law.

Alternative Dispute Resolution (ADR)

Alternative Dispute Resolution is mediated negotiation facilitated by a trained HMRC mediator who has not previously worked on the case. ADR is available alongside or instead of statutory review and is particularly useful where the dispute is factual or technical rather than legal, where direct correspondence has broken down, or where both parties are talking past each other. The mediator does not impose a decision - they help reach a negotiated outcome. Reported settlement rates are around 70% to 80% of accepted cases.

Postponing payment during appeal. Filing an appeal does not by itself suspend the duty to pay the assessed tax. Separately apply to HMRC under Section 55 TMA 1970 (for direct taxes) for a postponement of collection pending appeal. HMRC normally grants postponement for the disputed amount if the case has reasonable prospects.

9. Reasonable excuse and behaviour

"Reasonable excuse" is the statutory defence to most fixed and tax-geared penalties in the Self Assessment, PAYE, VAT and Schedule 36 regimes. The Upper Tribunal authority on the test is Perrin v HMRC [2018] UKUT 156 (TCC). Perrin establishes a four-step framework that every First-tier Tribunal decision references:

1. Identify the facts asserted to constitute the excuse.
2. Decide which of those facts are established on the evidence.
3. Decide objectively whether those established facts amount to a reasonable excuse.
4. Consider whether the taxpayer remedied the failure without unreasonable delay once the excuse ceased.

The objective standard rejects "honest belief" arguments - the question is what a reasonable taxpayer in the same circumstances would have done, not what the taxpayer subjectively thought. Excuses that typically succeed: serious illness with medical evidence, bereavement of a close family member shortly before the deadline, fire / flood / theft of records, documented postal disruption, HMRC system outage on the filing day, agent failure unknown to the taxpayer where the taxpayer was reasonably diligent. Excuses that typically fail: forgetting the deadline, finding the system difficult, lack of funds (expressly excluded by paragraph 23(2) of Schedule 56), and blanket reliance on an agent without checking.

For Schedule 24 inaccuracy penalties the relevant defence is "reasonable care" rather than reasonable excuse. The two are closely related but reasonable care is forward-looking (whether the conduct that led to the inaccuracy met the standard of a reasonable taxpayer) while reasonable excuse is backward-looking (whether unexpected events excused failure to meet a deadline). Reliance on a properly instructed competent adviser is normally reasonable care, though Hicks v HMRC made clear blind signing of whatever an adviser produces is not. See our HMRC penalties guide for the full reasonable-excuse framework.

10. Professional fee insurance and specialist advisers

Two practical questions every taxpayer under enquiry faces: who to engage as adviser, and how to pay for it.

Professional fee protection insurance

Most UK accountancy firms offer their clients an annual professional fee protection policy (typically branded "tax investigation insurance" or "fee protection"). The product covers the cost of the accountant's professional fees during an HMRC enquiry. Typical premium £150 to £300 per year for a sole trader, director or self-employed individual, with cover limits of £75,000 to £100,000 per claim. The policy pays the adviser's defence fees - it does not pay the underlying tax, interest or penalties (which remain the taxpayer's liability). Whether the policy is worthwhile depends on risk profile: high-income earners, landlords, contractors, anyone with offshore exposure, anyone in cash-handling sectors or anyone with volatile self-employed income is at meaningfully higher enquiry risk, and a single enquiry can pay for many years of premiums. PAYE-only employees with straightforward returns derive less value. Exclusions for COP9 fraud cases and for matters known at policy inception are universal - always read the wording.

Where to find a tax investigations specialist

The Chartered Institute of Taxation (CIOT) maintains a searchable find a Chartered Tax Adviser directory with members who hold the CTA qualification. ICAEW similarly runs the find a Chartered Accountant directory with filters for tax investigations specialism. For COP9 or criminal-risk cases a tax solicitor through the Law Society Find a Solicitor directory filtered for "tax investigations" or "criminal tax" is appropriate. For low-income taxpayers, TaxAid and the Low Incomes Tax Reform Group (LITRG) provide free guidance and casework. The HMRC enquiry experience itself is the strongest filter on adviser quality: ask any prospective adviser how many Section 9A enquiries, Schedule 36 notice challenges and COP8 / COP9 cases they have personally handled in the past 24 months. Specialist firms exist who handle nothing else.

11. Common triggers for enquiries

While HMRC does not publish its risk-scoring rules, both Tribunal decisions and HMRC's own Compliance Manual reveal consistent patterns. The following profiles are disproportionately represented in opened enquiries.

• High-income individuals. The High Net Worth Unit and the Wealthy and Mid-Sized Business Compliance Directorate focus on taxpayers with annual income over £200,000 or significant net wealth. Both run rolling reviews and regular enquiries on the population they monitor.
• Sudden income changes year on year. Large drops in declared self-employed profits, or sudden jumps that do not match prior-year trajectory, attract automatic risk flags. HMRC Connect cross-references PAYE data, dividend records and Companies House filings to validate the declared figure.
• Cash-handling businesses. Restaurants, takeaways, taxi drivers, building trades, market traders, hairdressers, tattoo studios and similar predominantly-cash sectors are subject to higher baseline risk scoring and periodic mass campaigns.
• R&D tax credit claims. HMRC has significantly tightened R&D enquiry activity since 2023 following systemic abuse of the SME R&D scheme. Any R&D claim, particularly for smaller companies in non-traditional R&D sectors, faces elevated enquiry risk.
• EIS / SEIS / VCT investment claims. Enterprise Investment Scheme claims and Venture Capital Trust claims trigger validation against the issuing company's HMRC advance assurance. Mismatches or claims against companies that have not received assurance routinely trigger enquiries.
• Rental property income. The Let Property Campaign has not closed; HMRC continues to cross-reference Land Registry, council tax records and tenancy deposit scheme data against Self Assessment returns. Any landlord with property visible to the Connect database who has not declared rental income on Self Assessment faces enquiry risk.
• Undeclared cryptocurrency. HMRC has received UK-resident customer data from Coinbase, Binance, Kraken and other major exchanges under information-exchange agreements. Crypto activity not matched to Self Assessment capital gains or trading income declarations triggers risk flags. See our UK crypto tax guide.
• Offshore connections. The Common Reporting Standard delivers UK-resident account data from over 100 jurisdictions every September. Any foreign account, foreign property income or foreign dividend not reflected in the relevant Self Assessment return is highly likely to be matched against HMRC records. See our UK residence (SRT) guide.
• IR35 and contractor patterns. Personal service companies operating with a small number of long-running engagements at a single end-client face elevated IR35 enquiry risk, particularly post-2021 reform where the end-client makes the status determination.
• Lifestyle / declared income mismatch. Visible assets in the Connect database (property purchases, vehicle registrations, credit profiles, foreign travel) that exceed what declared income could fund are a persistent risk trigger. The trigger is statistical - if your declared income is in the 30th percentile and your declared assets are in the 90th, the system notices.

12. Frequently asked questions

How will I know HMRC has opened a tax investigation into me?

You will receive a letter. For a Self Assessment enquiry the letter cites Section 9A Taxes Management Act 1970 and names the tax year under enquiry. For a PAYE / employer compliance check you receive a Compliance Check letter referencing Schedule 36 Finance Act 2008. For a COP8 (suspected tax avoidance) or COP9 (suspected fraud) case the letter is hand-delivered or sent by named officer and explicitly cites the relevant Code of Practice. HMRC does not open investigations by phone, text or email - any contact claiming to be an investigation by those channels is almost certainly a scam. Always check the officer name and reference against HMRC contact details on gov.uk before responding.

How far back can HMRC go in a tax investigation?

Three tiers under Section 36 Taxes Management Act 1970 and Section 34 of the same act. The normal time limit to issue a discovery assessment is 4 years from the end of the tax year in question - this catches ordinary mistakes and innocent omissions. The careless behaviour limit is 6 years, applying where HMRC can show the taxpayer (or their agent) failed to take reasonable care. The deliberate behaviour limit is 20 years, applying to anything HMRC can show was knowingly wrong, including deliberate concealment. Offshore matters within Schedule 7 Finance Act 2019 attract a 12-year assessment window even for non-deliberate behaviour. The clock runs from the end of the tax year being assessed, not from when HMRC discovered the issue.

What is the difference between COP8 and COP9?

COP8 (Code of Practice 8) is the procedure HMRC use when they suspect serious tax avoidance involving complex arrangements, but no criminal fraud. It is a civil investigation typically run by the Fraud Investigation Service or specialist counter-avoidance teams. COP9 (Code of Practice 9) is the Contractual Disclosure Facility - HMRC use it when they suspect deliberate tax fraud. The taxpayer is offered 60 days to admit the conduct and disclose it in exchange for HMRC not pursuing criminal prosecution. COP9 is a one-off offer; declining it (or being found to have concealed further fraud within an accepted COP9) opens the door to prosecution. Any taxpayer receiving a COP9 letter should engage a specialist tax investigations solicitor or accountant before responding.

Can I refuse a face-to-face meeting with HMRC?

Yes. There is no statutory obligation to attend an HMRC meeting during a Section 9A enquiry. HMRC frequently requests meetings because face-to-face questioning is more productive than written exchanges, but you (or your adviser) can decline and insist on written correspondence. Many advisers actively recommend declining meetings during early-stage enquiries because casual statements can be misconstrued and there is no agreed record. The exception is COP9 where a face-to-face opening meeting is part of the structured process. Schedule 36 information notices can compel the production of documents, but cannot compel oral testimony - you may attend a meeting and decline to answer specific questions.

What is a closure notice?

A formal HMRC document under Section 28A Taxes Management Act 1970 that ends an enquiry. The closure notice states either that no amendment is required (the return stands) or sets out the amendments HMRC propose to make. From the date of the closure notice you have 30 days to appeal in writing. Appealing converts the dispute into a formal appeal that can proceed to statutory review and then to the First-tier Tribunal. If you do not appeal within 30 days, the closure notice becomes final and the amended tax becomes due. Taxpayers can also apply to the First-tier Tribunal under Section 28A(4) for a direction requiring HMRC to issue a closure notice if HMRC is dragging an enquiry on without reasonable cause.

Does HMRC investigate everyone or just high earners?

Both, but with different priorities. HMRC opens a small percentage of Self Assessment returns to random enquiry every year (the exact ratio is not published but historically estimated under 1%). Risk-based enquiries dominate by volume and target high-risk profiles: high-income individuals over £200k, taxpayers with significant offshore connections, cash-business sectors (restaurants, takeaway, construction, tradespeople), landlords with rental income, contractors and IR35 cases, R&D tax credit claims, EIS / SEIS / VCT claims and unexplained wealth flagged by the Connect database. HMRC Connect cross-references over 30 data sources including Land Registry, DVLA, bank reporting under the Common Reporting Standard, eBay / Vinted / Airbnb sales data and credit reference files.

Should I get a professional adviser for an HMRC enquiry?

Yes for anything beyond a single-item aspect enquiry. The reasons are practical, not defensive. A specialist adviser knows what HMRC is statutorily entitled to ask, what is irrelevant or out-of-scope, how to scope an information request narrowly, and how to negotiate penalty bands under Schedule 24. They also act as a buffer, preventing casual statements being treated as evidence. For COP8 and COP9 cases a specialist is effectively mandatory - the technical complexity and the stakes (potential prosecution) make self-representation extremely risky. The Chartered Institute of Taxation (CIOT), ICAEW and Law Society maintain searchable directories of specialists. TaxAid and LITRG provide free guidance for low-income taxpayers who cannot afford private representation.

What is professional fee insurance and is it worth it?

Professional fee protection insurance (sometimes called tax investigation insurance) covers the cost of accountant or solicitor fees when HMRC opens an enquiry. Most UK accountancy firms offer it to clients as an annual add-on, typically £150 to £300 per year for a sole trader or director, with cover limits of £75,000 to £100,000 per claim. It does not pay the underlying tax or penalties - only the professional defence costs. Whether it is worth it depends on risk profile: high-income earners, landlords, contractors, anyone with offshore income or volatile self-employment is at meaningfully higher enquiry risk and the policy can pay for itself with a single enquiry. PAYE-only employees with straightforward returns derive less value. Read the policy carefully - exclusions for COP9 fraud cases and for matters known at policy inception are universal.

Can I disclose unreported income to HMRC voluntarily?

Yes, and the penalty consequences are significantly better than waiting to be caught. HMRC operates several structured disclosure facilities. The Worldwide Disclosure Facility (WDF) handles offshore income and gains. The Let Property Campaign covers undeclared rental income. The Digital Disclosure Service handles ad-hoc unreported income for any tax. For suspected fraud, the Contractual Disclosure Facility (CDF / COP9) is the route. All disclosure facilities require full disclosure of the unreported position, payment of the tax plus interest, and a penalty calculated under Schedule 24 - but typically at the unprompted-disclosure floor of the band, which on a careless inaccuracy is 0% (vs 15% prompted) and on a deliberate inaccuracy is 20% (vs 35% prompted). Anyone considering disclosure should take advice before contacting HMRC, particularly for offshore matters where Schedule 24A enhanced penalties apply.

What if HMRC asks for documents I do not have?

A Schedule 36 information notice can only compel production of documents in your possession or power. If documents do not exist, or have been legitimately destroyed in line with normal record-retention practice, you have a statutory defence. The duty is to respond in writing explaining what records exist, what does not, and why. Failure to comply attracts the initial £300 penalty and £60 per day continuing penalty under paragraph 39 of Schedule 36, but reasonable excuse applies (paragraph 45) and includes genuine inability to access records. For documents held by a third party such as an overseas bank or former employer, you may need to demonstrate reasonable steps taken to obtain them. The Crystal Trustees v HMRC line of cases confirms genuine inability constitutes reasonable excuse where the taxpayer has actively tried to remedy.

How long does an HMRC investigation take?

Highly variable. A simple aspect enquiry into a single item (eg a specific expense claim, a clearly identifiable employment income discrepancy) is often resolved within 3 to 6 months. A full enquiry into a complete Self Assessment return typically runs 9 to 18 months. Complex enquiries involving multiple tax years, offshore matters or detailed business records can run 2 to 5 years. COP8 avoidance investigations average 18 to 36 months. COP9 fraud investigations under the CDF run on a structured 60-day initial disclosure deadline followed by typically 12 to 24 months to complete the outline disclosure, scoping document and final settlement. The First-tier Tribunal adds another 6 to 18 months if the case escalates to formal appeal. Throughout, the taxpayer can apply for a closure notice under Section 28A(4) to force HMRC to conclude if progress stalls.

Will HMRC tell me why they opened an enquiry?

Not usually, and they are not required to. The Section 9A enquiry notice will identify the tax year being enquired into but typically does not state what triggered the enquiry. HMRC routinely refuse Freedom of Information Act requests for the trigger as commercially sensitive (their risk-scoring methodology) and prejudicial to ongoing investigations. Sometimes a separate letter narrows the scope (eg "we want to look at your property income for 2024/25") which gives a partial indication. For COP8 and COP9 cases the opening letter is more specific about the suspected conduct. In practice, the trigger is often inferable from what HMRC then asks about - their information requests under Schedule 36 reveal the area of interest even when the opening letter is generic.

Related explainers and tools

• HMRC penalties guide (Sch 24, Sch 36, late filing, late payment)
• Self Assessment step-by-step guide
• UK residence (Statutory Residence Test) guide
• UK landlord tax guide
• UK crypto tax guide
• UK tax deadlines for 2026/27
• How UK tax works (primer)
• UK tax glossary A to Z
• SalaryTax methodology and sources

This page is editorial guidance based on HMRC publications and tax legislation retrieved 23 May 2026. It is not tax advice. Tax investigation procedures, time limits and penalty bands change with each Finance Act - always verify the current position on the relevant gov.uk page and on the HMRC Enquiry Manual before relying on these figures. If HMRC has opened an enquiry against you, particularly any COP8 or COP9 investigation, engage a qualified Chartered Tax Adviser, accountant or solicitor with tax investigations experience as a priority. Where this guide differs from a primary HMRC source, the HMRC source governs.