Compliance check in one paragraph: a Section 9A notice gives HMRC formal authority to investigate your tax return. They can request records, ask questions, and ultimately adjust your tax liability. The process is governed by published HMRC guidance and Taxes Management Act 1970. You have rights including the right to professional representation, the right to know what HMRC is looking at, and the right to appeal any adjustment. Most checks close within 12-18 months. Settling cooperatively with quality disclosure typically attracts penalties at the lower end of the range; obstruction or non-cooperation widens both the scope and the penalty.
What is a Section 9A enquiry?
The Taxes Management Act 1970 gives HMRC the power to "enquire into" any Self Assessment return. Mechanics:
- HMRC issues a Section 9A notice within 12 months of the filing date (so for a 2024/25 return filed in January 2026, they have until January 2027 to open an enquiry)
- If the return is filed late, the enquiry window extends accordingly
- The notice specifies what aspects HMRC is enquiring into — could be "general" or specific
- Once open, the enquiry runs until HMRC issues a "closure notice" or you've appealed and won
- HMRC has the right to request records, ask questions, and visit premises if relevant
Variants for other taxes:
- Section 12AC: partnership returns
- Schedule 36: information request notice (separate authority)
- VAT enquiries: covered by VATA 1994 and CEMA 1979
- Corporation Tax: Schedule 18 FA 1998
The three types of compliance check
1. Aspect enquiry (most common)
HMRC asks about a specific aspect of your return — e.g., a particular expense claim, a property income figure, a rental allowance.
- Typically completed in 3-12 months
- Records requested are usually limited to the specific item
- Penalty exposure typically £0 to a few thousand
- Most can be handled without professional representation if records are clean
2. Full enquiry
HMRC examines the entire return — all income, all deductions, all reliefs.
- Typically runs 12-24 months
- Significant document request: bank statements, business records, contracts, correspondence
- Penalty exposure can be substantial
- Professional representation strongly recommended
3. Cross-tax enquiry
HMRC looks at multiple tax years and tax types together (e.g., 5 years of SA + 3 years of VAT).
- Can run 2-3 years
- Indicates HMRC suspects deliberate behaviour or systemic non-compliance
- Often involves an HMRC face-to-face meeting
- Professional representation essential
What triggers a compliance check?
- Risk profiling by HMRC Connect (their internal AI). The largest single source of enquiries.
- Random selection. About 1-2% of enquiries are genuinely random.
- Data discrepancy. Bank/employer/agent data not matching your return.
- Specific tip-offs. Whistleblowers, divorce filings, related-party enquiries.
- Sector campaigns. HMRC regularly targets sectors — landlords, online sellers, contractors, restaurant trade, etc.
- Following a nudge letter. If you didn't respond satisfactorily.
- Late or unusual filing. Repeated late filing or sudden swings in declared income.
Your rights during a compliance check
- Right to a fair process. HMRC must follow the Compliance Check Framework and Customer Charter.
- Right to representation. You can appoint an accountant, tax adviser, or solicitor at any point.
- Right to know what's being checked. The Section 9A notice must specify the scope.
- Right to time to respond. Typical 30-day response windows; you can request reasonable extensions.
- Right to appeal. You can appeal HMRC's information requests, formal decisions, and final assessments to the First-tier Tax Tribunal.
- Right to a closure notice. If HMRC seems to be dragging the enquiry, you can apply to the Tribunal for a direction that HMRC must issue a closure notice.
- Right to a review. If HMRC reaches a decision you disagree with, you can ask for an internal HMRC review by an independent officer before going to tribunal.
How to respond — practical steps
- Don't ignore the notice. Acknowledge receipt promptly. Failure to respond is a separate offence.
- Identify what's being checked. Read the notice carefully. Specific aspect or full enquiry?
- Gather records. Pull bank statements, invoices, contracts, receipts for the relevant year(s) and topic.
- Consider professional advice. For aspect enquiries with clean records, you can often handle directly. For full or cross-tax enquiries, get help.
- Respond proportionately. Provide what's asked, with brief explanatory cover, but don't volunteer unrelated information.
- Keep meticulous records of all correspondence. Dates, telephone calls, content of each exchange.
- Don't agree to face-to-face meetings without preparation. Always confirm in writing what will be covered, who will attend, and whether your adviser can be present.
- Track time limits. The enquiry window (12 months from filing) limits HMRC's authority to open, but once open they can take years.
The closure notice
The enquiry ends when HMRC issues a closure notice under Section 28A:
- "No amendment": HMRC accepts your return as filed. No adjustments.
- "Amendment with figures": HMRC proposes specific adjustments and assesses additional tax (or refund) accordingly.
- "Closing with penalty assessment": if HMRC concludes there was careless or deliberate error, penalties are added.
You have 30 days from the closure notice to appeal. If you don't appeal, the closure becomes final and the tax is due.
Penalty bands
| Behaviour | Unprompted | Prompted |
|---|---|---|
| Reasonable care | 0% | 0% |
| Careless | 0-30% | 15-30% |
| Deliberate (not concealed) | 20-70% | 35-70% |
| Deliberate and concealed | 30-100% | 50-100% |
"Reasonable care" is the safe harbour — if you took reasonable care in preparing your return (got advice where appropriate, kept records, used HMRC guidance), no penalty even if the return is later found to be wrong. This is the most powerful defence.
Reduction within band: HMRC reduces toward the lower end based on "telling" (admitting promptly), "helping" (providing information freely), and "giving" (giving access to records).
Worked example: aspect enquiry into rental property
Mr P submits 2024/25 SA in January 2026. HMRC opens a Section 9A enquiry in November 2026, specifically asking about declared rental income on a property in Manchester. They've cross-referenced Land Registry and council tax records.
Mr P's response:
- Confirms receipt within 10 days
- Gathers tenancy agreement, rental statements, repair invoices, mortgage interest records
- Provides records to HMRC with a covering letter explaining the income figure
- HMRC asks one follow-up question about a £4,000 expense claim
- Mr P provides supporting invoice; HMRC accepts
- Closure notice issued: "No amendment" — return accepted
Total enquiry time: 5 months. No professional fees beyond Mr P's own time. No penalty.
Common compliance check mistakes
- Ignoring the notice. Triggers automatic penalty and widens the enquiry.
- Volunteering excess information. Stick to what was asked.
- Getting defensive or aggressive in correspondence. Professional, factual responses get the best outcomes.
- Hiring expensive representation for trivial matters. A £500 accountant fee for a £200 adjustment is poor value.
- Not getting representation for serious matters. A £5,000 adviser fee for a £50,000 penalty exposure is exceptional value.
- Settling too quickly to "make it go away". If you believe HMRC's adjustment is wrong, appeal it.
- Forgetting the right to internal review. Free, often produces a better outcome than tribunal.
Sources
Related HMRC enquiry content
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