What Triggers an HMRC Enquiry — And How to Reduce Your Risk
For many business owners, the idea of an HMRC enquiry is a major concern. In HMRC’s own language, this is usually called a compliance check. HMRC says a compliance check is used to make sure you are paying the right amount of tax at the right time and claiming the right allowances and reliefs. HMRC also makes clear that most checks are based on identified risks, but some are random, so it is more accurate to talk about factors that may increase scrutiny rather than guaranteed triggers.
The good news is that many of the common risk factors can be reduced with better records, cleaner filings, and clearer explanations. Good compliance does not guarantee HMRC will never ask questions, but it can reduce avoidable risk and make any check much easier to manage.
What is an HMRC enquiry?
An HMRC enquiry, or compliance check, is when HMRC reviews your tax position. HMRC says this can include your taxes, your accounts and tax calculations, your Self Assessment tax return, your Company Tax Return, and your PAYE records if you employ people. HMRC may write to you, call you, ask for documents, or arrange a visit.
That does not automatically mean HMRC thinks you have done something wrong. It means HMRC wants to understand your figures, verify records, or clarify part of your tax position. HMRC’s own guidance says some checks involve requesting information, discussing the figures with you, and then establishing the correct tax position before the check is closed.
Common factors that may increase HMRC scrutiny
1. Large or unexplained changes in figures
If income, profit, expenses, or VAT figures change sharply from one period to the next, that can increase the chance of questions being asked. HMRC says most checks are started where a risk has been identified, so figures that look unusual, inconsistent, or out of pattern may attract attention if they cannot be explained properly. This is an inference from HMRC’s risk-based approach rather than a published list of exact numerical triggers.
Examples could include a sudden drop in profit, a large increase in expenses, or margins changing significantly without any obvious commercial reason. None of those automatically mean there is a problem, but they are the sort of changes that are easier to defend when the underlying records and explanation are clear.
2. Repeated low profits or ongoing losses
Low profits do not automatically trigger an enquiry, but persistent losses or unusually weak results may prompt HMRC to ask whether the business records are complete and whether the figures reflect genuine commercial activity. Again, this is not an HMRC checklist item published as a formal trigger, but it follows from HMRC’s risk-based approach and its focus on checking the correct tax position.
Where a business has a genuine reason for low profits, such as investment, difficult trading conditions, or expansion costs, the key point is being able to explain it clearly and support it with records.
3. Weak records or poorly supported expense claims
Expense claims are one of the easiest areas to get wrong. HMRC says you must keep records of all sales and income, all business expenses, VAT records if you are VAT-registered, and PAYE records if you employ people. HMRC also says your records must be accurate and you must be able to identify business transactions and show the records if asked.
That means high travel costs, large home-use claims, vague miscellaneous expenses, or any costs that are not supported properly can become harder to defend if HMRC asks questions. The issue is often not just the amount claimed, but whether the claim is organised, evidenced, and easy to explain.
4. Late or incorrect filings
Repeated late or inaccurate filings can increase scrutiny. HMRC’s VAT guidance says the frequency of VAT visits can depend in part on whether you have submitted late or incorrect VAT returns before. HMRC also imposes penalties for late Self Assessment returns and late Company Tax Returns, which makes repeated filing failures a clear compliance risk even where they do not automatically lead to a full enquiry.
This is one of the simpler risk areas to reduce. Filing on time and getting the numbers right will not remove all risk, but it avoids creating a poor compliance pattern for no good reason.
5. Mismatches with third-party or external data
HMRC does not rely only on what you put on a return. HMRC’s own data guidance says it collects information from direct reports by taxpayers, intermediaries acting for them, employers, online platforms, other parts of government, and other administrative sources. That means mismatches between your return and external information can create questions.
This matters more now than many people realise. For example, HMRC says digital platforms may have to collect and report seller information, and HMRC also has specific guidance for people earning income through online platforms. So if income is visible elsewhere but does not appear correctly on a return, it is easier for HMRC to spot inconsistencies.
6. Random checks still happen
This is the point many articles get wrong. HMRC says most checks are based on identified risks, but some are selected at random. HMRC’s manuals say random checks are used partly to test its understanding of risk and partly as a deterrent. So even a well-run business with tidy records can still be selected occasionally.
That does not mean compliance is pointless. It means good compliance is about reducing avoidable risk and making any check manageable, not trying to guarantee you will never be contacted.
How to reduce your risk
1. Keep accurate and organised records
HMRC says you must keep accurate records of income and expenses and be able to show them if asked. That alone makes record-keeping your first line of defence. If your records are clear, transactions are easy to trace, and evidence is easy to produce, it becomes much easier to respond to questions calmly and quickly.
2. Separate business and personal finances
HMRC says you must be able to identify business transactions. In practice, separate business and personal finances make that much easier. This is a practical recommendation rather than a direct HMRC instruction to open a separate bank account, but it follows from HMRC’s record-keeping requirement and the need to distinguish business transactions clearly.
3. Be consistent — and document genuine changes
Not every large movement in the figures is suspicious. But if turnover, profit, VAT, or expense levels move sharply, it helps to have a clear reason and supporting documentation ready. HMRC’s approach is risk-based and proportionate to the risk involved, so unexplained movements are naturally more difficult than explained ones.
4. File accurately and on time
Late or incorrect filings can create unnecessary risk. HMRC’s own guidance on VAT checks and filing penalties makes that clear enough. Staying on top of deadlines is one of the simplest ways to avoid making your compliance record look worse than it needs to be.
5. Get professional help before problems build up
HMRC says you can have an accountant or legal adviser with you during a compliance check. In practice, getting advice before an issue turns into a formal check is often even more valuable. This is not because an adviser makes you immune from scrutiny, but because they can often spot weak records, filing problems, or unclear treatment before HMRC does.
What happens if HMRC selects you?
HMRC says it will usually write or phone to tell you what it wants to check. It may ask for information or documents, discuss matters with you, visit your business, or ask you to attend a meeting. HMRC then reviews the material and establishes the correct tax position before closing the check.
Possible outcomes range from no changes at all to adjustments, interest, or penalties in more serious cases. The better your records and explanations, the easier it usually is to deal with the process.
Preparation reduces stress
The biggest difference between a stressful HMRC enquiry and a manageable one is usually preparation. Good records, timely filings, and clear explanations do not just reduce risk before a check. They also make the check far easier to handle if HMRC does get in touch.
At Merranti, we help business owners keep records cleaner, spot obvious risk areas earlier, and respond properly if HMRC opens a compliance check. If you are worried about whether your figures, records, or claims would stand up to scrutiny, it is usually better to review them before HMRC asks the questions.
