Your HMRC enquiry letter response is the single most important step you will take. An HMRC enquiry letter is one of the most stressful pieces of post an SME owner can receive. Most people open it and re-read it twice. Then they do one of two things. Some panic and respond the same day. Others put it aside ‘until they know what to do’. Both reactions cost money. The correct response in the first 30 days is narrow, specific, and different from what the letter itself suggests you should do.
HMRC Enquiry Letter Response: What HMRC Is Really Doing
Every HMRC enquiry letter response starts with understanding the letter itself. HMRC must formally notify you in writing before opening an enquiry. The letter you hold will be one of three types. A ‘Connect risk letter’ is a prompt — it tells you HMRC’s data-matching system has flagged an inconsistency and invites you to review your return. By contrast, a ‘nudge letter’ is a more pointed invitation to correct a specific suspected error. Meanwhile, a Section 9A notice — formally titled ‘Notice of enquiry under Section 9A of the Taxes Management Act 1970’ — is the legal opening of an enquiry.
Only a Section 9A notice is an enquiry in the formal legal sense. Connect risk letters and nudge letters are softer HMRC tactics designed to produce voluntary amendments without the cost of a formal enquiry. But they are not neutral. Ignoring or mishandling any of the three escalates the matter automatically. HMRC opened approximately 300,000 enquiries in 2025–26 — up 28% on the previous year — and the overwhelming majority started with a letter that looked softer than it was.
How Your HMRC Enquiry Letter Response Affects Your Business
Your HMRC enquiry letter response must land inside 30 days. The 30-day clock on an HMRC enquiry letter has legal teeth. If the letter is a Section 9A notice opening an aspect or full enquiry, HMRC typically sets a 30-day deadline for you to produce documents or respond to questions. Missing that deadline allows HMRC to issue an Information Notice under Schedule 36 of the Finance Act 2008. This is a legal power to demand documents. Penalties start at £300, plus £60 per day for non-compliance.
The financial exposure depends on the enquiry type. An aspect enquiry into a specific item typically resolves in 3–6 months, with tax adjustments from £0 to £15,000 for most SMEs. A full enquiry covering multiple years can run 12–18 months, with adjustments from £5,000 to £100,000+. Where HMRC concludes behaviour was deliberate, penalties of up to 100% of unpaid tax apply, and the assessment window extends to 20 years. For a typical SME director, a poorly handled full enquiry can destroy 2–3 years of accumulated post-tax income.
The hidden cost of an HMRC enquiry letter response is time. An enquiry consumes 40–80 hours of owner or finance team time over its lifespan, plus professional fees. Fee Protection Insurance — typically £150–£400 per year — covers £100,000+ of defence costs if triggered; but you cannot buy it after the letter arrives.
What You Must (and Must Not) Do
What to Do in the First 72 Hours
- Read the letter in full and identify the type — Connect risk letter, nudge letter, or Section 9A notice. The heading of the letter makes this clear.
- Note the response deadline. For a Section 9A notice, it is typically 30 days from the letter date — not the date you received it.
- Locate the relevant Self Assessment return(s) or company accounts referenced in the letter and identify the specific aspect HMRC is asking about.
- Call a specialist investigation adviser before responding. Most offer a free initial consultation and can tell you whether the matter is low-risk or serious within one call.
- Stop amending, shredding, or ‘tidying’ any records. Preserving everything in its current state is a legal obligation under Schedule 36.
What Not to Do
- Never phone HMRC to discuss the letter. Call logs become part of the case file, and unguarded statements on a recorded HMRC line are used against taxpayers routinely.
- Avoid respond in writing using the template the letter suggests. The template invites you to admit specific errors and accept penalty categories — both of which are negotiable with professional representation.
- Resist send documents HMRC has not specifically requested. Over-disclosure in the opening weeks hands HMRC evidence for new lines of enquiry.
- Skip amend the return in question before taking advice. A bare amendment without a structured voluntary disclosure can trigger the harshest penalty category — ‘deliberate, concealed’ — rather than mitigate it.
- Refrain from assume the letter is a mistake. HMRC does send occasional errors in bulk mailings, but the default assumption should be that you are in scope and act accordingly.
Aspect Enquiry vs Full Enquiry — The Practical Difference
The distinction matters because it changes everything about how you respond.
| Feature | Aspect Enquiry | Full Enquiry |
|---|---|---|
| Scope | One specific area of one return | Entire return, potentially multiple years |
| Typical duration | 3–6 months | 12–18 months |
| Documents requested | Limited to the aspect | Full books, records, bank statements |
| Typical tax adjustment | £0–£15,000 | £5,000–£100,000+ |
| Escalation risk | Can become full enquiry | Can become COP9 (civil fraud) investigation |
| Rights under TMA 1970 | Same — you may close the enquiry via Tribunal application | Same |
| Professional fee range (defended) | £3,000–£8,000 | £15,000–£50,000 |
An aspect enquiry can be closed down quickly with tight, evidence-based responses — and doing so prevents it expanding into a full enquiry. A full enquiry needs a defence strategy, scoping challenges to limit HMRC’s information requests, and active negotiation of penalty categories throughout. Each requires a different response tempo.
Your Rights — TMA 1970 and Schedule 36
Under the Taxes Management Act 1970, you have specific rights that are rarely set out clearly in HMRC’s opening letter. You may request a review of any HMRC decision by an independent HMRC review officer before matters reach Tribunal. You may apply to the First-tier Tax Tribunal for a direction to close the enquiry. This applies where you believe it has run too long or become unfocused. Section 28A of the TMA 1970 gives the Tribunal power to force closure. Under Schedule 36, you may challenge any Information Notice that requests documents outside the scope of the enquiry or information you do not reasonably hold. These powers exist to balance HMRC’s authority — but most taxpayers never use them because they do not know they exist.
Our HMRC Enquiry Letter Response Process
From the moment you instruct us, all correspondence with HMRC goes through our office. We register an authorisation under form 64-8, which means HMRC must write to us, not to you, for everything related to the enquiry. Our immediate actions are clear. First, a full scope review of the letter. Second, evidence gathering on the specific aspect queried. Third, drafting a proportionate response that answers what has been asked — and only what has been asked — and agreeing a communication rhythm with HMRC that gives us control of the pace.
Our team includes former HMRC officers who worked inside Compliance, Investigation, and the Solicitor’s Office. That matters because we know how HMRC builds a case, where their evidence is typically thin, and which arguments they are allowed to drop once pressed. Our clients routinely see penalty reductions of 40–80% compared with initial HMRC proposals, and approximately 70% of our aspect enquiries close with no tax adjustment.
Key Facts at a Glance
- Standard enquiry response window: 30 days from the date on the letter
- Schedule 36 penalty for non-compliance with Information Notice: £300 initial plus £60/day
- Aspect enquiry typical duration: 3–6 months
- Full enquiry typical duration: 12–18 months
- HMRC enquiries opened in 2025–26: approximately 300,000 (up 28% year-on-year)
- Maximum penalty for deliberate behaviour: 100% of tax owed
- Assessment window: 4 years (reasonable care), 6 years (careless), 20 years (deliberate)
Speak to Tax Guard Today
Before you respond to HMRC, call us. A free, confidential consultation will tell you exactly what type of letter you hold, what is actually at stake, and what the next step should be. The first 30 days set the tone for the rest of the enquiry — and the difference between a well-handled opening and a mishandled one is often the entire outcome of the case.
Common Questions About HMRC Enquiry Letters
Q: How do I know if my HMRC letter is a formal enquiry?
A: A formal enquiry is opened by a Section 9A notice under the Taxes Management Act 1970, and the letter explicitly says so in the heading. Connect risk letters and nudge letters are softer prompts — they do not open a formal enquiry, but they signal HMRC is reviewing your position. Any of the three should prompt a professional call before you respond. Responding incorrectly to a nudge letter routinely triggers the formal enquiry the letter was designed to make unnecessary.
Q: What is the 30-day deadline for?
A: The 30-day clock on a Section 9A notice is the period HMRC expects you to produce initial documents or answer opening questions. Missing it triggers HMRC’s right to issue a Schedule 36 Information Notice, which is a legal demand with penalties of £300 plus £60 per day for non-compliance. You can request an extension, but only with a specific reason — ‘still taking advice’ rarely qualifies without a professional representative asking on your behalf.
Q: Should I phone HMRC to clarify what they want?
A: No. Phone calls to HMRC are logged and become part of the enquiry file. Anything you say can be used to expand the enquiry or escalate the behaviour category. If clarification is needed, it should be sought in writing through a professional representative, who can frame the question without committing you to admissions. HMRC’s own procedures require officers to record and refer back to taxpayer phone calls throughout an investigation.
Q: Can I just pay what HMRC thinks I owe and be done with it?
A: Paying is rarely a clean exit. HMRC’s opening position is almost always higher than the final settlement — in our experience, initial tax and penalty proposals are reduced by 30–70% during negotiation. Paying quickly also locks in the penalty category HMRC originally assigned. If you are in a position to settle, structure it through a formal disclosure process to preserve rights to reduced penalties and to close the assessment window properly.
Q: Will HMRC tell me what information they already have about me?
A: No. HMRC is not obliged to disclose what Connect data or Financial Institution Notice returns they hold, and they routinely do not. Assume HMRC has your complete bank data, Companies House filings, Land Registry records, crypto exchange data, and overseas tax authority exchanges (via the Common Reporting Standard). A good defence response is built on the assumption that HMRC’s evidence is comprehensive.
Q: Does Fee Protection Insurance cover everything?
A: Fee Protection Insurance covers professional fees for defending most HMRC enquiries — typically up to £100,000 of fees per claim. It does not cover the tax itself, the interest, or penalties. It usually excludes criminal investigations and pre-existing enquiries. Policies bought before an enquiry opens are the only ones HMRC cannot retrospectively invalidate — once a letter arrives, you cannot buy cover for that matter.