What Is an HMRC Tax Investigation?
An HMRC tax investigation (formally called an enquiry or compliance check) is a review by HMRC into a person’s or business’s tax affairs. HMRC has the legal power to check that the right amount of tax has been paid and that returns have been filed correctly.
Investigations can be triggered by specific concerns or selected at random. They range from a simple check on one aspect of a return to a full-scale investigation covering multiple years of accounts and personal finances.
Types of Investigation
Full Enquiry
A full enquiry examines every aspect of your tax return and accounts. HMRC may request:
- Complete business records and bank statements
- Personal bank statements
- Records of all income sources
- Explanations for discrepancies between declared income and lifestyle
Full enquiries are usually opened when HMRC suspects serious irregularities or fraud.
Aspect Enquiry
An aspect enquiry focuses on one specific area of a tax return, such as:
- A particular expense claim
- A source of income
- A specific relief or allowance
- The treatment of a particular transaction
Most HMRC enquiries are aspect enquiries. They are less intrusive than full enquiries and typically resolve more quickly.
Compliance Checks
HMRC also conducts compliance checks to verify specific obligations:
| Type | What It Covers |
|---|---|
| PAYE compliance | Correct operation of PAYE, NIC, and benefits in kind |
| VAT compliance | VAT return accuracy, input tax claims, record keeping |
| Corporation tax | CT600 accuracy, deductions, reliefs claimed |
| Self-assessment | Income tax return accuracy and completeness |
| Employer compliance | National Insurance, expenses, and benefits |
Code of Practice 9 (COP 9)
The most serious type of investigation is opened under Code of Practice 9. This is used when HMRC suspects deliberate tax fraud. Under COP 9, HMRC offers the opportunity to make a full disclosure under the Contractual Disclosure Facility (CDF) in exchange for not pursuing criminal prosecution.
What Triggers an Investigation?
HMRC uses sophisticated data analysis to identify returns that may contain errors. Common triggers include:
- Random selection — a proportion of returns are selected randomly each year
- Anomalies in the return — figures that do not match industry norms or previous years
- Information from third parties — banks, employers, HMRC’s Connect system, and overseas tax authorities
- Tip-offs — reports from members of the public, disgruntled employees, or ex-partners
- Living beyond declared means — lifestyle that does not match reported income
- Inconsistent data — mismatches between different tax returns (e.g., VAT vs income tax)
- Late filing — consistently filing returns late
- Large or unusual claims — such as significant tax-deductible expenses or R&D relief claims
- Cash-heavy businesses — trades where cash transactions are common
HMRC Connect
HMRC’s Connect system is a powerful data-matching tool that cross-references information from:
- Bank and building society records
- Land Registry records
- Companies House filings
- Overseas tax authority data exchange
- Online marketplace and payment platform records
- Social media activity
How an Investigation Starts
Opening Letter
HMRC opens an enquiry by issuing a formal notice of enquiry letter. For self-assessment returns, this must be issued within 12 months of the filing date (or the actual submission date, if later).
For returns involving potential loss of tax through carelessness, HMRC can go back up to 6 years. For deliberate understatement, the window extends to 20 years.
Information Requests
HMRC will request documents and information. You are legally required to comply with a formal information notice. Typical requests include:
- Bank statements — personal and business
- Sales invoices and purchase receipts
- Contracts and agreements
- Payroll records
- VAT records and calculations
- Capital asset records
- Tax computations and working papers
Your Rights During an Investigation
You have several important rights:
- Professional representation — you can appoint an accountant or tax adviser to deal with HMRC on your behalf
- Right to appeal — you can appeal against assessments, penalties, and information notices
- Reasonable time — HMRC must give you a reasonable period to provide information
- Confidentiality — HMRC must handle your information securely
- Proportionality — HMRC should not request information that is excessive or unnecessary
- Right to a review — you can request an internal review of HMRC’s decision before appealing to the tax tribunal
Responding to an Investigation
Step 1: Seek Professional Advice
Engage a qualified tax adviser or accountant as soon as you receive an enquiry notice. They can manage communication with HMRC, identify potential issues, and negotiate on your behalf.
Step 2: Gather Records
Compile all records requested by HMRC. Thorough accounting records make this process significantly easier.
Step 3: Review the Return
Check the return under enquiry for any errors, voluntary or involuntary. If errors are found, it is usually better to disclose them proactively — this can reduce penalties.
Step 4: Respond Within Deadlines
Reply to HMRC’s information requests within the stated timeframes. Failing to respond can result in daily penalties or HMRC making an estimated assessment based on the information available.
Outcomes
No Additional Tax Due
If HMRC is satisfied that the return is correct, they issue a closure notice confirming no further action is needed.
Additional Tax Plus Interest
If errors are found, HMRC will assess the additional tax due. Interest is charged from the date the tax should have been paid.
Penalties
If the error was more than innocent, HMRC charges penalties based on the behaviour that led to the error:
| Behaviour | Penalty Range (Unprompted Disclosure) | Penalty Range (Prompted Disclosure) |
|---|---|---|
| Reasonable care | No penalty | No penalty |
| Careless | 0% to 30% | 15% to 30% |
| Deliberate | 20% to 70% | 35% to 70% |
| Deliberate and concealed | 30% to 100% | 50% to 100% |
Penalties are calculated as a percentage of the potential lost revenue (the additional tax due). Making a voluntary disclosure before HMRC contacts you significantly reduces the penalty.
Suspension of Penalties
For careless errors, HMRC can suspend penalties for up to 2 years, subject to conditions (such as improving record keeping or implementing new controls). If the conditions are met, the penalty is cancelled.
Time Limits
| Situation | Assessment Window |
|---|---|
| Normal enquiry | 4 years from the end of the tax year |
| Careless error | 6 years from the end of the tax year |
| Deliberate error | 20 years from the end of the tax year |
| Failure to notify liability | 20 years from the end of the tax year |
Costs of an Investigation
Even if no additional tax is due, investigations are costly in terms of:
- Professional fees — accountant or tax adviser fees for handling the enquiry
- Management time — gathering records and responding to requests
- Stress — the investigation process can be lengthy and disruptive
Fee protection insurance is available and covers professional fees in the event of an HMRC enquiry. Many accountancy firms offer this as part of their service package.
Reducing Investigation Risk
While random selection cannot be avoided, you can reduce the risk of being targeted by:
- Filing all returns on time via self-assessment or corporation tax
- Ensuring returns are accurate and consistent with previous years
- Claiming only legitimate tax-deductible expenses
- Maintaining comprehensive accounting records
- Complying with Making Tax Digital requirements
- Responding promptly to any HMRC correspondence