Guide
Handle an HMRC Self Assessment enquiry
What happens when HMRC opens an enquiry into your Self Assessment return, what triggers one, your rights, how to respond, and when to get professional help.
An HMRC enquiry (also called a compliance check) is a formal examination of your tax return. Receiving an enquiry notice does not mean HMRC thinks you have done something wrong - some enquiries are random. However, you must respond within the deadlines or face penalties.
This guide explains the different types of enquiry, what triggers them, your rights throughout the process, and how to respond effectively.
What triggers an enquiry?
HMRC selects returns for enquiry using a combination of risk assessment, data matching, and random selection. Common triggers include:
- Inconsistent figures: Your income or expenses have changed significantly from previous years without explanation
- Industry benchmarks: Your profit margins or expense ratios are unusual compared to similar businesses in your sector
- Third-party data: Information from banks, letting agents, online platforms, or other sources does not match what you reported
- Late filing or errors: Returns filed late or with corrections attract more scrutiny
- Cash-intensive businesses: Businesses handling significant cash payments face higher audit rates
- Random selection: HMRC selects a proportion of returns at random regardless of risk indicators
- Informant tip-offs: HMRC acts on information received from third parties
Important: HMRC cannot tell you why your return was selected. You will only know it is a random enquiry if HMRC specifically states this.
Types of HMRC enquiry
Not all enquiries are the same. The scope determines how much of your affairs HMRC will examine and how long the process takes.
Aspect enquiry vs full enquiry
Most Self Assessment enquiries are aspect enquiries - HMRC has a specific question about one part of your return. These are usually resolved in a few months with the right records. A full enquiry examines your entire return and all supporting records, and can take 12 months or longer.
HMRC will tell you in the opening letter whether it is a full or aspect enquiry. If they do not specify, assume it is an aspect enquiry and ask HMRC to confirm the scope in writing.
Time limits for HMRC to open an enquiry
HMRC cannot open an enquiry indefinitely. There are strict time limits, and understanding them helps you know when you are in the clear.
What this means in practice: If you filed your 2024/25 return on 15 November 2025, HMRC has until 15 November 2026 to open a standard enquiry. After that date, they can only reassess your return through a discovery assessment, which requires them to show they could not reasonably have known about the insufficiency from the information you provided.
Your rights during an enquiry
You have significant rights throughout the process. Knowing them helps you manage the enquiry effectively and push back if HMRC oversteps.
How to respond to an enquiry
When you receive the opening letter
- Do not panic. An enquiry is not an accusation. Stay calm and professional in all communications.
- Note the deadline. HMRC will give you a deadline to respond (usually 30 days). Missing it can lead to penalties.
- Read carefully. Identify exactly what HMRC is asking for. Provide what is requested and nothing more.
- Consider professional help. If the enquiry covers significant amounts or complex matters, engage an accountant or tax adviser early. Tax investigation insurance (often included in accountancy fees) may cover the cost.
During the enquiry
- Provide records promptly. Delays can extend the enquiry and raise suspicion. Keep copies of everything you send to HMRC.
- Answer only what is asked. Volunteering information beyond the scope of the enquiry can open new lines of investigation.
- Keep records of all communications. Note dates, names of HMRC officers, and what was discussed in phone calls.
- Request meetings in writing. If HMRC wants a meeting, you can ask for the agenda in advance and have your adviser present.
If HMRC finds errors
If the enquiry reveals that you owe more tax, HMRC will issue an assessment for the additional amount plus interest from the original due date. Penalties may also apply depending on the nature of the error.
Voluntary disclosure reduces penalties
If you discover an error during the enquiry (or before HMRC does), disclosing it voluntarily always results in a lower penalty. An unprompted disclosure (before HMRC raises the issue) attracts the lowest penalty range. A prompted disclosure (after HMRC has identified the issue) attracts higher penalties but is still treated more favourably than non-cooperation.
If the error was genuinely careless and you cooperate fully, HMRC can suspend the penalty for up to 2 years. If you meet the conditions (such as improving your record keeping), the penalty is cancelled at the end of the suspension period.
How an enquiry ends
HMRC closes an enquiry by issuing a closure notice. This sets out any amendments to your return and any additional tax, penalties, or interest due. If HMRC is taking unreasonably long, you can apply to the Tax Tribunal for a direction requiring HMRC to issue a closure notice.
Possible outcomes:
- No change: HMRC is satisfied with your return. No additional tax, no penalties.
- Additional tax due: HMRC amends your return. You owe the extra tax plus interest. Penalties may apply if the error was careless or deliberate.
- Refund due: Occasionally, an enquiry reveals you overpaid tax. HMRC will issue a repayment with interest.
Appealing the outcome
If you disagree with the closure notice, you have 30 days to appeal. The same appeal process applies as for other HMRC decisions.
Record keeping and enquiry protection
Good records are your best defence in an enquiry. If you cannot support a figure on your return with records, HMRC may estimate the correct figure - and their estimates tend to be higher than the actual amount.
When to get professional help
You can handle a straightforward aspect enquiry yourself if you have good records and the amounts are small. However, consider engaging a tax adviser if:
- The enquiry is a full enquiry covering your entire return
- The potential additional tax exceeds £5,000
- HMRC suggests the error may be deliberate
- You receive a Code of Practice 9 letter (suspected fraud)
- You are unsure how to respond to HMRC's questions
- The enquiry has been going on for more than 6 months with no resolution
Tax investigation insurance: Many accountancy practices include fee protection insurance in their annual fees. This covers the cost of professional representation if HMRC opens an enquiry. Check whether your accountant offers this, or consider standalone tax investigation insurance (typically £100-£300 per year).
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Read the enquiry notice carefully
Identify whether it is a full or aspect enquiry, what information HMRC is requesting, and the response deadline (usually 30 days).
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Gather your records
Collect all records relevant to the items HMRC is querying - invoices, receipts, bank statements, mileage logs, and any other supporting documents.
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Consider professional representation
If the enquiry is complex, involves significant amounts, or suggests deliberate errors, engage a tax adviser. Check whether your accountant's fees include tax investigation insurance.
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Respond within the deadline
Provide exactly what HMRC has asked for, clearly organised and referenced. Keep copies of everything you send. Do not volunteer information beyond what was requested.
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Disclose any errors voluntarily
If you discover an error, disclose it to HMRC immediately. Unprompted voluntary disclosure attracts the lowest penalty rates and demonstrates good faith.
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Appeal if you disagree with the outcome
You have 30 days from the closure notice to appeal. You can request a statutory review by HMRC or appeal directly to the First-tier Tax Tribunal.
Do not ignore an enquiry notice
Failing to respond within the deadline can result in HMRC issuing an information notice under Schedule 36 of the Finance Act 2008. Non-compliance with an information notice carries a fixed penalty of £300, plus daily penalties of up to £60 per day.