A brown envelope from HMRC announcing an "enquiry" or "compliance check" can make the steadiest taxpayer's stomach drop. But take a breath: an enquiry is not an accusation, and it is certainly not a verdict. It is a request to look more closely at part — or occasionally all — of your tax position. Handled calmly and correctly, most enquiries close without drama.
Every year HMRC opens enquiries into individuals, the self-employed, landlords, and companies. Some are prompted by something specific; a small number are genuinely random. The worst response is to panic, ignore the letter, or improvise answers. The best response is to understand what is actually being asked, respond within the deadlines, and get the right help early. This article explains how enquiries work and how to navigate one without making it worse.
What an HMRC enquiry actually is
HMRC uses the umbrella term "compliance check" for the various ways it examines whether the right amount of tax has been paid. A formal "enquiry" is the statutory version that follows a self-assessment return, opened by a notice within strict time limits. The scope can vary enormously, which is why the first task is always to read the letter carefully and identify exactly what HMRC is looking at.
Broadly, enquiries fall into a few categories. A random check is exactly that — your return has been selected as part of HMRC's routine quality-assurance work, with nothing wrong implied. An aspect enquiry targets one specific item or figure: a particular expense claim, a single source of income, or one relief you have claimed. A full enquiry examines your entire return and supporting records, and is more likely where HMRC perceives broader risk. Most enquiries are aspect-based and resolve quickly once the point is clarified.
Separately, where HMRC suspects serious or deliberate tax fraud, it may use its civil investigation of fraud procedure under Code of Practice 9 (COP9), which offers the Contractual Disclosure Facility — a route to settle suspected fraud civilly through full disclosure rather than criminal prosecution. A COP9 letter is a serious matter and should never be answered without specialist representation.
An enquiry letter is a question, not a conclusion. The taxpayers who fare worst are rarely those who made an honest mistake — they are those who panic, guess, or go silent.
What commonly triggers an enquiry
HMRC increasingly relies on its "Connect" data system, which cross-references information from banks, employers, the Land Registry, online marketplaces, overseas tax authorities, and more. When the picture does not add up, an enquiry can follow. Understanding the common triggers helps explain why a letter has arrived — and, more usefully, how to avoid future ones.
No single factor guarantees an enquiry, but these are the patterns HMRC's systems and officers most often flag:
- Inconsistencies and anomalies — figures that swing sharply year on year, or margins and expenses well outside the norm for your trade.
- Undeclared or under-declared income — rental income, side businesses, online sales, dividends, or foreign income that HMRC sees through third-party data but not on your return.
- Industry risk — cash-heavy sectors and trades with a higher historic error rate attract closer attention.
- Information from third parties — data from banks, employers, the Land Registry, payment processors, and other tax authorities, plus the occasional tip-off.
- Persistent lateness or errors — repeatedly late returns, frequent amendments, or round-number estimates that suggest records are not being kept.
- Random selection — sometimes there is no trigger at all, and your return is simply part of HMRC's routine sample.
Your rights and how to respond
An enquiry is a structured process with rules that bind HMRC as well as you. Knowing your rights keeps the process fair and proportionate, and a measured response almost always produces a better outcome than a defensive or evasive one.
- Check HMRC's authority. HMRC's power to request information is not unlimited. A formal request must relate to your tax position and be reasonably required; you are entitled to understand the legal basis for each request and to question anything that goes beyond it.
- Respond within the deadlines. Enquiry letters set time limits for replies. If you need more time — to gather records or take advice — ask for an extension in writing rather than letting a deadline pass in silence.
- Keep everything in writing. Confirm telephone conversations by email or letter, keep copies of everything you send, and maintain a clear record of dates and documents. A clean paper trail protects you if a point is later disputed.
- Answer the question — and only the question. Provide what is asked, accurately and completely, but do not guess, speculate, or volunteer additional information beyond the scope of the enquiry. Inaccurate off-the-cuff answers cause more problems than they solve.
- Get professional representation early. An accountant or tax solicitor can deal with HMRC on your behalf, frame disclosures correctly, and prevent an aspect enquiry from drifting unnecessarily into a full one. Bringing in help at the start is far cheaper than repairing missteps later.
The possible outcomes
Enquiries end in one of a handful of ways, and most are far less alarming than the opening letter suggests. The outcome turns largely on whether anything was actually wrong and, if so, why.
The best result is no change: HMRC accepts your return as filed and closes the enquiry, sometimes with a closure notice confirming there is nothing to alter. Where an under-payment is found, you will owe the additional tax, usually with interest charged on the amount that was paid late. Beyond that, HMRC may apply penalties, and this is where behaviour matters most.
Penalties for inaccuracies are scaled according to the behaviour behind the error. A genuine mistake made despite taking reasonable care may attract no penalty at all, while a careless error sits at the lower end, and a deliberate — or deliberate and concealed — error sits at the most serious end. Crucially, penalties are reduced by the quality of disclosure: an unprompted disclosure made before you had reason to think HMRC was on to you, together with full cooperation, attracts the largest reductions. Because the exact percentages change and depend on the facts, do not rely on a figure from memory — check the current rules on GOV.UK or take advice.
If an enquiry uncovers errors across earlier years, HMRC may also expect a wider correction. Where past mistakes exist, there are structured disclosure options — such as HMRC's Digital Disclosure Service and the various disclosure facilities — that allow you to come forward voluntarily, which almost always produces a better penalty position than waiting to be found out.
- An HMRC enquiry or compliance check is a request to look more closely at your tax — not an accusation or a verdict.
- Enquiries range from random checks and narrow aspect enquiries to full enquiries; serious suspected fraud follows the separate COP9 route, which needs specialist help.
- Common triggers include inconsistencies, undeclared income, industry risk, and third-party data — though some selections are genuinely random.
- Respond within the deadlines, keep everything in writing, answer only what is asked, and bring in professional representation early.
- Penalties scale by behaviour from careless to deliberate and are reduced by unprompted disclosure and cooperation — always confirm current figures on GOV.UK.
How Crejj & Partners can help
Our Tax Filing & Advisory team acts for individuals and businesses from the moment an enquiry letter arrives. We read the letter against HMRC's actual powers, manage correspondence and deadlines on your behalf, and ensure every response is accurate, complete, and confined to what is properly being asked. Where past errors come to light, we advise on the right disclosure route to minimise penalties, and where serious matters such as COP9 are in play, we provide the specialist representation those cases demand. Just as importantly, we help clients keep clean, defensible records so that future enquiries — if they come at all — close quickly and quietly. If a letter has landed on your doormat, the time to speak to us is now.
This article is provided for general information only and does not constitute legal or tax advice or create a solicitor–client relationship. Tax rules and figures change; always confirm current rules on GOV.UK or with an adviser. Crejj & Partners is a fictional firm presented for illustrative purposes on this website.