HMRC Investigation: What to Expect and How to Prepare

The Accounted Business Team·14 March 2026·8 min read

Getting a letter from HMRC saying they want to look into your tax affairs is enough to ruin anyone's week. But an investigation does not automatically mean you have done something wrong, and it does not have to be a disaster — especially if your records are in good shape.

This guide explains the different types of HMRC investigation, what triggers them, what you can expect during the process, your rights, and how to come through it with as little pain as possible.

Types of HMRC Enquiry

HMRC uses two main types of investigation for individuals and small businesses.

Aspect Enquiry

This is the most common type. HMRC picks one specific part of your tax return to check — maybe a particular expense claim, a source of income, or a figure that does not look right. The enquiry is limited to that aspect. If everything checks out, it goes no further.

Full Enquiry

This is the deep dive. HMRC looks at your entire tax return and underlying records. Every source of income, every expense, every figure. Full enquiries are less common but more serious. They usually happen when HMRC has reason to believe there are significant errors or deliberate understatement of income.

Compliance Checks

Beyond formal enquiries, HMRC also carries out compliance checks. These are often focused on a specific issue — for example, checking that employers are operating PAYE correctly, or that VAT returns match sales records. They are less formal than a full enquiry but still require your cooperation and records.

What Triggers an Investigation?

HMRC opens enquiries for several reasons. Some are random. Many are not.

Random Selection

HMRC selects a proportion of tax returns at random for checking. There is nothing you can do to avoid this — it is the luck (or bad luck) of the draw. Random enquiries are designed to keep everyone honest and to help HMRC understand where mistakes are most common.

Targeted Selection

This is more common. HMRC's computer systems use data analytics to flag returns that look unusual. Things that can trigger a closer look include:

Figures that do not match third-party data. HMRC receives information from banks, employers, property platforms, and payment processors. If the income on your return does not match what these sources report, expect questions.

Significant changes from previous years. If your turnover drops by 40% or your expenses double without an obvious reason, that stands out.

High expenses relative to income. If you are claiming expenses that eat up 90% of your turnover, HMRC may wonder whether all those expenses are legitimate.

Industry benchmarks. HMRC knows what typical profit margins look like for different trades. A self-employed plumber reporting a 5% profit margin when the industry average is 30% will attract attention.

Tips from informants. Yes, this happens. Disgruntled ex-partners, former employees, or business rivals can and do report suspected tax evasion to HMRC. There is even a dedicated hotline for it.

Cash-heavy businesses. If your trade deals heavily in cash (think hairdressers, takeaways, market traders), HMRC applies extra scrutiny because cash is harder to trace.

Late or missing returns. Consistently filing late, or not filing at all, is a red flag.

What HMRC Can Request

During an enquiry, HMRC has broad powers to ask for information and documents. They can request:

Bank statements (business and personal)
Invoices and receipts
Contracts and agreements
Payroll records
VAT records
Till rolls and booking records
Digital records and software data
Emails and correspondence relating to business transactions

HMRC can also visit your business premises, though they must give reasonable notice for a routine visit. In serious fraud cases, they can turn up unannounced with a warrant.

You are legally required to provide the information requested within a reasonable time (usually 30 days, but this can be negotiated). Failing to provide information without a reasonable excuse can lead to daily penalties of £10 per day, rising to up to £300 for continued non-compliance.

The Investigation Process

Step 1: The Opening Letter

You receive a letter from HMRC telling you they are opening an enquiry. It will explain what aspect of your return they are looking at (for an aspect enquiry) or that they are carrying out a full review.

Do not panic. Read the letter carefully. Note the deadline for your response. If you have an accountant, contact them immediately.

Step 2: Gathering Information

HMRC will ask you to provide specific documents and information. Respond within the deadline with exactly what they ask for — no more, no less. Do not volunteer extra information unless asked.

Step 3: HMRC Review

HMRC reviews what you have provided. This can take weeks or months. They may come back with follow-up questions or requests for more documents.

Step 4: Meeting (If Required)

For more serious enquiries, HMRC may want a face-to-face meeting. You have the right to have your accountant or tax adviser present, and you should always take them up on this. Never attend an HMRC meeting alone.

Step 5: Findings and Settlement

HMRC will tell you their findings. If they believe additional tax is due, they will explain their calculation and give you the opportunity to agree or dispute it. Most enquiries are settled by agreement. If you cannot agree, you can appeal to a tax tribunal.

Your Rights During an Investigation

You have important rights throughout the process:

The right to be represented. You can have an accountant, tax adviser, or solicitor deal with HMRC on your behalf.
The right to appeal. If you disagree with HMRC's decision, you can request a formal review or appeal to the First-tier Tribunal.
The right to complain. If you believe HMRC has handled the enquiry unreasonably, you can complain through their formal complaints process or escalate to the Adjudicator's Office.
The right to confidentiality. HMRC cannot discuss your affairs with third parties without your permission (with some legal exceptions).
Protection against unreasonable demands. HMRC must act proportionately. They cannot demand every document you have ever created if the enquiry is about one specific item.

Penalties

If HMRC finds errors in your return, the penalty depends on the nature of the error:

Careless Errors

Mistakes made through lack of reasonable care. Penalties range from 0% to 30% of the additional tax due.

Deliberate Errors

Errors you made on purpose but did not try to hide. Penalties range from 20% to 70% of the additional tax due.

Deliberate and Concealed Errors

Errors you made on purpose and actively tried to cover up. Penalties range from 30% to 100% of the additional tax due.

Penalty Reductions

Penalties are reduced based on your cooperation. HMRC looks at three factors:

Telling: Did you tell HMRC about the error before they found it?
Helping: Did you help HMRC work out the correct figures?
Giving access: Did you provide full access to your records?

Full cooperation can bring even a deliberate penalty down to its minimum. Stonewalling pushes it to the maximum.

Unprompted vs Prompted Disclosure

If you discover an error and tell HMRC before they start investigating, this is an unprompted disclosure and carries much lower penalties. If HMRC finds the error during an enquiry, it is prompted, and the penalties are higher.

How Good Records Protect You

The single best thing you can do to prepare for a potential HMRC investigation is to keep thorough, accurate, up-to-date records. If HMRC asks for evidence and you can produce clean, organised records quickly, it does three things:

It shows you are running your affairs seriously and carefully, which makes HMRC less likely to dig deeper.
It speeds up the process. Enquiries that drag on for years usually do so because the taxpayer cannot find their records.
It limits penalties. Even if there is an error, demonstrating that you took reasonable care with your record keeping can reduce penalties to zero.

This is where your bookkeeping system becomes your best friend. Accounted's AI bookkeeper Penny creates an automatic audit trail of every transaction — matched to bank feeds, linked to scanned receipts, and categorised correctly. If HMRC comes knocking, you can pull up a complete, timestamped record of your financial history in minutes, not months.

Compare that to digging through a carrier bag of receipts and trying to remember what a £47.50 charge from 18 months ago was for.

What to Do If You Receive an Enquiry Letter

Stay calm. Most enquiries end without any additional tax being due.
Contact your accountant or tax adviser immediately. Do not try to handle it yourself.
Do not ignore it. Failing to respond makes everything worse.
Gather your records. Pull together everything relevant to the period and items being investigated.
Respond within the deadline. Provide what is asked for, accurately and on time.
Keep copies of everything you send to HMRC.

Prevention Is Better Than Cure

You cannot avoid a random enquiry, but you can massively reduce your chances of a targeted one. File on time. Report all your income. Claim only legitimate expenses. Keep your records straight. And make sure the figures on your return make sense in the context of your industry.

Accounted gives you year-round peace of mind by keeping your financial records complete, organised, and audit-ready. Penny logs every transaction automatically and keeps your receipts matched and stored. Start your free trial today — because the best time to prepare for an HMRC enquiry is long before one arrives.

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