HMRC does not investigate at random. It uses data, risk models, and third-party intelligence to decide who to look at. Knowing the common triggers helps you spot problems early.
Disclaimer: This article is for general information only. It doesn’t constitute tax advice. If HMRC has contacted you, speak to a qualified accountant immediately.
What are the most common triggers for an HMRC investigation?
HMRC uses a mix of automated data analysis and manual referrals to select who to investigate. The most common triggers include inconsistencies between your tax return and third-party data, unexplained jumps in income or expenses, and patterns that don’t match others in your industry.
These triggers are not secret. HMRC publishes guidance on risk indicators, and its data systems are wide-ranging. Here are the main ones:
Figures that don’t match third-party data
HMRC receives data from banks, employers, pension providers, and Companies House. It compares this data against your tax return automatically. If your return shows lower income than your bank deposits suggest, that mismatch triggers a review.
Landlords are a common example. HMRC receives data from letting agents and property platforms. If your rental income return doesn’t line up with what those platforms report, you’ll attract attention.
Inconsistencies between years
A sudden drop in income or a large spike in expenses raises questions. If your gross profit margin drops from 45% to 20% with no explanation, HMRC will want to know why.
This is especially relevant for cash businesses. If your declared income falls while your lifestyle expenditure stays the same, HMRC has tools to assess what you likely earned.
Returns that don’t match your industry
HMRC uses industry benchmarks. If your tax return shows expenses or margins that look unusual compared to similar businesses, that’s a flag.
For example, if most sole traders in your sector report a 30 to 40% gross margin and yours is consistently 5%, HMRC will notice.
What are the red flags that put you on HMRC’s radar?
The biggest red flags are late or missing returns, offshore assets not declared, cash-heavy businesses with low declared income, and large round-number claims that look like estimates rather than real figures.
Specific patterns HMRC looks for include:
Late or amended returns. Filing late repeatedly suggests disorganised record-keeping. Filing an amendment soon after your original return can also attract scrutiny if the change is significant.
High expense claims relative to income. Claiming most of your income as business expenses, especially for home office, travel, or entertainment, is a known risk indicator.
Round-number entries. Figures like £10,000 for travel or £5,000 for office supplies look like guesses. Real business expenses have receipts and specific amounts.
Tips from third parties. Former employees, business partners, or competitors can report suspected tax evasion to HMRC. These reports are taken seriously and often lead to investigations.
Offshore accounts or foreign income. HMRC shares data with over 100 countries under the Common Reporting Standard. Undisclosed offshore income is increasingly easy for HMRC to detect.
How does HMRC choose who to investigate?
HMRC uses a system called Connect to cross-reference data from over 30 sources. These include DVLA, Land Registry, Companies House, banks, and social media. Connect flags mismatches between declared income and lifestyle indicators.
Connect is automated. It runs continuously and scores risk across millions of taxpayers without human intervention. Only the highest-risk cases get referred to a human inspector.
Beyond Connect, HMRC runs specific campaigns targeting sectors it believes have compliance problems. Construction, the hospitality trade, and online sellers have all been the subject of targeted campaigns in recent years.
If HMRC identifies a sector where reported margins are consistently below what the evidence suggests is possible, it launches a disclosure campaign and then follows up on those who didn’t come forward.
How likely are you to be investigated by HMRC?
Fewer than 1 in 100 tax returns lead to a formal investigation. But the risk is much higher for certain groups: self-employed people, company directors, landlords, and anyone who uses a cash-based business model.
An investigation doesn’t always mean HMRC suspects fraud. Many start as routine checks, called aspect enquiries, where HMRC asks about one specific line on your return. These often resolve quickly if your records are in order.
Full investigations, which cover your entire tax return, are rarer. They’re more likely when HMRC has evidence of a serious discrepancy or receives a third-party tip.
The best defence is clean records. If you can explain every figure on your return with receipts, bank statements, and invoices, an HMRC enquiry is manageable.
What should you do if you get a letter from HMRC?
Don’t ignore it. HMRC letters have deadlines. Missing them can turn a routine check into a formal investigation.
Read the letter carefully. An aspect enquiry only covers the specific issue mentioned. A full enquiry covers everything. The letter will usually make this clear.
Don’t respond without taking advice. What you say in your first response sets the tone for the entire process. An accountant experienced in HMRC investigations can help you respond accurately and avoid making the situation worse. Our guide explains what an HMRC letter means and what to do next.
If you think there is an error in your previous returns, it’s often better to disclose this proactively. HMRC treats voluntary disclosures more favourably than errors it finds itself. You can get help with an HMRC enquiry from a qualified accountant before you respond.
How can you reduce your risk of an HMRC investigation?
Keep accurate records throughout the year, not just at tax return time. HMRC can request up to 6 years of records in a standard enquiry, and up to 20 years if it suspects intentional evasion.
File on time, every time. Late filings increase your risk score in HMRC’s systems. Not sure if you’re required to file? Check if you need to send a Self Assessment tax return using HMRC’s online tool.
Review your Self Assessment return before submission. Check that your figures are consistent with last year, that expense claims are proportionate, and that all income sources are included.
If you’re unsure about any element of your tax return, especially around expenses, offshore income, or capital gains, take professional advice before you file. A small mistake now is much cheaper to fix than an investigation later.
DASA can help if HMRC makes contact
If you receive a letter from HMRC or have concerns about your tax position, speak to us early. We work with businesses and individuals through HMRC enquiries, from initial correspondence through to resolution.
Get a quote and we’ll send you our current pricing for DASA’s HMRC investigation service.