An HMRC enquiry letter is one of the few tax events that turns an abstract compliance obligation into an immediate, personal pressure. The letter has a deadline, the language is formal, and the instinct is either to panic or to fire back everything HMRC has asked for. Both are mistakes. This guide explains what HMRC enquiries actually are, the different types and how serious each is, your rights, and — most importantly — what to do (and not do) when a letter lands.
📌 If you have just received a letter
- Don't ignore it — deadlines are strictly enforced and missing them increases penalties
- Don't over-respond — sending everything at once can widen the enquiry
- Identify the Code of Practice — COP1, COP8 and COP9 are very different in seriousness
- Preserve records — never edit, delete or "tidy" documents; destruction is a separate offence
- Get representation before responding — especially for anything beyond a routine check
What an HMRC enquiry actually is
Most enquiries are compliance checks — a formal review of a taxpayer's records and returns conducted under Schedule 36 of the Finance Act 2008. This is the routine, civil form of enquiry, almost always conducted under Code of Practice 1 (COP1). It is not an accusation of fraud; HMRC checks returns for a range of reasons, from random selection to a specific figure that looks out of line with expectations.
A check can be "aspect" (a narrow focus on one or two issues — a single deduction, an R&D claim, a property disposal) or "full" (a comprehensive review of all returns for a year). Most checks are aspect-based; full checks are reserved for higher-risk cases or follow from concerning aspect findings. An enquiry that starts on one tax or one year can extend to adjacent years or other taxes if what HMRC finds raises further questions — which is exactly why the initial response matters so much.
The types of enquiry — and how serious each is
The single most important thing to establish from the letter is which Code of Practice applies. It determines everything about how you should respond.
| Code | What it means | Seriousness |
|---|---|---|
| COP1 | Routine compliance check into records and returns | Civil, routine — often resolved in correspondence |
| COP8 | Suspected significant tax avoidance (no allegation of fraud yet) | Serious — handled by the Fraud Investigation Service |
| COP9 | Suspected deliberate tax fraud; offers the Contractual Disclosure Facility | Most serious — specialist representation essential |
The escalation runs in one direction. A COP1 check that uncovers material concealment can shift to COP9; the reverse rarely happens, and once HMRC has escalated there is generally no return to the softer track. COP8 and COP9 are both run by HMRC's Fraud Investigation Service and demand experienced representation from the outset — for COP9, a tax solicitor, because unlike an accountant a solicitor's advice attracts legal professional privilege.
HMRC's powers — and their limits
Under Schedule 36, HMRC can issue a formal information notice compelling production of specific documents. These carry a deadline (typically 30 days) and non-compliance triggers penalties of £300 plus £60 per day. But the powers are not unlimited:
- A formal notice can be appealed within 30 days on grounds including irrelevance or disproportionate scope
- Under COP1, meetings are voluntary — you can choose to respond entirely in writing through your adviser (this changes under COP9, where disclosure meetings form part of the process)
- Requests made informally (rather than by formal notice) can be declined, though unreasonable refusal often prompts a formal notice
- You need only answer specific questions truthfully within the enquiry's scope — cooperation does not mean volunteering unnecessary material
Received an HMRC enquiry letter?
The first response shapes the whole enquiry. We can review the letter, identify the Code of Practice, and handle HMRC correspondence on your behalf.
How far back can HMRC go?
For a return under self assessment or corporation tax self assessment, HMRC generally has 12 months from the filing date to open an enquiry — the "normal enquiry window". Beyond that window, HMRC can still act through a discovery assessment, and how far back it can reach depends on behaviour:
| Behaviour | How far back HMRC can assess |
|---|---|
| Innocent error (reasonable care taken) | 4 years |
| Careless (failure to take reasonable care) | 6 years |
| Deliberate (or failure to notify / offshore) | Up to 20 years |
This is why the characterisation of behaviour — innocent, careless or deliberate — is often the real battleground in an enquiry. It drives both the number of years HMRC can reach back over and the level of penalty, so how the position is presented from the start genuinely matters.
What to do when a letter arrives
The right sequence is calm and deliberate, not reactive:
- Read it carefully and identify the Code of Practice and the deadline. A routine COP1 aspect check and a COP9 fraud investigation call for completely different responses.
- Don't respond in a rush. The instinct to send everything immediately can hand HMRC material outside the original scope and widen the enquiry. Equally, don't let a deadline pass — if you can't meet it, a short extension can often be agreed.
- Preserve all records — tax returns, accounts, bank statements, correspondence, contracts. Do not edit or delete anything.
- Consider whether an unprompted disclosure is appropriate where you already know of an error — a well-handled voluntary disclosure usually attracts lower penalties than something HMRC finds itself.
- Instruct appropriate representation. For a routine check your usual accountant may suffice; for anything complex, or COP8/COP9, specialist tax representation is effectively required.
An enquiry is, at its core, a negotiation conducted under rules — about scope, about behaviour, and about the eventual settlement. Handled well from the first letter, most routine checks resolve in correspondence without drama. Handled badly, a narrow aspect check can widen into a full review of several years. This is precisely the kind of moment where having someone who has sat on the technical side of HMRC dealings — and knows what to concede, what to challenge, and what simply not to volunteer — changes the outcome. For businesses, it is one of the clearest trigger points for bringing in specialist tax support.
✅ Key takeaways — HMRC enquiries
- Most enquiries are routine compliance checks under Schedule 36 (COP1) — civil, not an accusation of fraud
- Establish the Code of Practice first: COP1 (routine), COP8 (avoidance), COP9 (suspected fraud) are worlds apart
- HMRC's Schedule 36 information notices carry a 30-day deadline and £300 + £60/day penalties — but can be appealed on scope grounds
- The enquiry window is 12 months from filing; discovery reaches 4 years (innocent), 6 (careless) or 20 (deliberate)
- Don't over-respond and don't tidy records — both make things worse
- Get representation before responding; for COP8/COP9 it is essential, and for COP9 a solicitor (for legal privilege)
Frequently asked questions
What should I do if I receive an HMRC enquiry letter?
Read it carefully, identify the Code of Practice (COP1, COP8 or COP9) and the deadline, and preserve all records without editing anything. Don't respond in a rush — over-responding can widen the enquiry — but don't miss the deadline. For anything beyond a routine check, get specialist representation before you reply.
What is the difference between COP1, COP8 and COP9?
COP1 is a routine civil compliance check into records and returns. COP8 is a more serious investigation into suspected tax avoidance, run by the Fraud Investigation Service. COP9 is reserved for suspected deliberate fraud and offers the Contractual Disclosure Facility — it requires specialist legal representation.
How far back can HMRC investigate?
The normal enquiry window is 12 months from the filing date. Beyond that, a discovery assessment can reach back 4 years for an innocent error, 6 years for careless behaviour, and up to 20 years for deliberate behaviour or failure to notify.
Do I have to attend a meeting with HMRC?
Under COP1, meetings are voluntary — you can respond entirely in writing through your adviser. Formal Schedule 36 notices can compel production of documents but not attendance at meetings for most purposes. The position changes under COP9, where disclosure meetings form part of the process.
What is a Schedule 36 information notice?
A formal notice under Schedule 36 of the Finance Act 2008 compelling you to produce specific documents, usually within 30 days. Non-compliance triggers penalties of £300 plus £60 per day. A notice can be appealed within 30 days on grounds such as irrelevance or disproportionate scope.
Should I use my accountant or a specialist?
For a routine COP1 check, your usual accountant may be enough. For complex enquiries, or anything under COP8 or COP9, specialist tax representation is effectively required — and for COP9, a tax solicitor, because a solicitor's advice attracts legal professional privilege that an accountant's does not.