HMRC selects cases for investigation using a combination of risk profiling, data matching and random selection. Specific triggers include:

• Inconsistencies in returns. Figures that are out of line with prior years, industry norms or information held by HMRC from third parties, banks, employers, land registry, companies house.
• Unusually low declared profits for the level of turnover or lifestyle indicators visible to HMRC.
• Late or irregular filing patterns, these suggest a disorganised approach to compliance that may indicate wider problems.
• Third-party information. HMRC receives data from banks, letting agents, online platforms (including eBay, Airbnb and Etsy), overseas tax authorities and employers.
• Industry sector risk. HMRC operates ‘Connect’, a sophisticated data analysis system, and runs campaigns targeting sectors or activities where non-compliance is believed to be common.
• Tip-offs. HMRC operates an anonymous reporting line. Tips from former employees, business partners or members of the public do trigger investigations.
• Random selection. A proportion of investigations are genuinely random, no specific reason, simply part of HMRC’s compliance programme.

There is no guaranteed way to avoid investigation. However, keeping clean records, filing accurately and on time, and operating through a properly maintained accounting system significantly reduces the risk.

HMRC uses the term ‘enquiry’ to describe the formal process of examining a tax return. The term ‘investigation’ is more commonly used for broader, more serious examinations of a taxpayer’s affairs.

An enquiry is opened under Section 9A of the Taxes Management Act 1970 (for Income Tax) or Schedule 18 of the Finance Act 1998 (for Corporation Tax). HMRC has a 12-month window to open a formal enquiry into a return from the date it is filed. Outside that window, HMRC can only raise an assessment where it can demonstrate a failure to notify, fraudulent conduct, or negligent behaviour.

Enquiries can be:

• Aspect enquiries. Focused on one or more specific items in the return, a particular expense, a specific transaction or a claimed relief.
• Full enquiries. A comprehensive examination of the entire return and the underlying records.

A Code of Practice 9 (COP9) investigation is a separate process used where HMRC suspects fraud. It is the most serious form of investigation and carries different procedural rules and significantly higher potential consequences.

HMRC’s ability to investigate and raise assessments is subject to time limits, which vary depending on the nature of any error or omission:

• Normal time limit: 4 years from the end of the tax year or accounting period. This applies where there is no loss of tax or where the taxpayer has taken reasonable care.
• Careless behaviour: 6 years from the end of the relevant period.
• Deliberate behaviour: 20 years from the end of the relevant period.
• Failure to notify a liability to tax: 20 years.

These limits apply to assessments raised by HMRC. A formal enquiry into a return must be opened within 12 months of the filing date for that return. The extended limits apply to assessments made outside the enquiry window, known as discovery assessments.

In practice, HMRC rarely goes back more than six years unless there is clear evidence of deliberate behaviour. However, the 20-year limit is a genuine risk for serious cases.

The records HMRC requests depend on the scope and focus of the investigation. In a full enquiry, HMRC will typically request:

• Business bank statements for all accounts, including personal accounts if there is evidence of business income passing through them.
• Sales invoices, purchase invoices and receipts.
• Cash records, till rolls or point-of-sale records where cash is received.
• Payroll records, including RTI submissions and PAYE payment records.
• VAT records and returns.
• Director’s loan account records.
• Contracts with significant customers or suppliers.
• Personal bank statements and credit card statements, particularly where HMRC is assessing the lifestyle and spending patterns of a business owner.

HMRC has significant powers to require the production of documents. Failure to produce documents without reasonable excuse can result in penalties. Documents held by third parties, including banks and accountants, can also be obtained by HMRC through formal notice.

Do not destroy or alter records once you are aware that an investigation is underway or anticipated. Destruction of records in the context of an investigation is a serious criminal offence.

The duration of an HMRC investigation varies enormously and depends on its scope, the complexity of the issues, the co-operation of the taxpayer and the availability of HMRC’s own resources.

Aspect enquiries involving a single, straightforward issue can sometimes be resolved within a few months. Full enquiries into complex businesses can take two to five years, or longer in serious cases involving fraud.

Factors that shorten investigations:

• Clean, well-organised records that can be produced promptly.
• Full and prompt co-operation with HMRC’s information requests.
• Professional representation that manages the process and communicates effectively with HMRC.

Factors that lengthen investigations:

• Poor or incomplete records.
• Disputes about the interpretation of evidence.
• Multiple years under review.
• Related investigations into connected parties, spouses, business partners or associated companies.

From a practical perspective, even an investigation that concludes with a small or nil adjustment is disruptive, stressful and costly in professional fees. Prevention, through accurate returns, good records and timely filing, is always preferable.

Taxpayers have significant rights during an HMRC investigation, which are often not fully exercised:

• Right to professional representation. You are entitled to appoint an accountant, tax adviser or tax inspector to act on your behalf. HMRC must correspond with your representative rather than approaching you directly once a formal authorisation is in place.
• Right to know why you are being investigated. HMRC should explain the nature of its concerns, though it is not required to disclose all of its intelligence.
• Right to challenge unreasonable information requests. If HMRC requests documents or information that are not relevant to the enquiry or that would be unduly onerous to produce, this can be challenged.
• Right to appeal. If HMRC raises an assessment that you disagree with, you have the right to appeal, initially to HMRC’s own review process, and then to the First-tier Tax Tribunal.
• Right to a statutory review. Before appealing to the Tribunal, you can request an independent review of HMRC’s decision by a separate HMRC officer who was not involved in the original enquiry.

Throughout an investigation, you are not required to volunteer information beyond what HMRC has specifically requested. You are however required to answer questions truthfully, providing false information to HMRC is a criminal offence.

A Code of Practice 9 (COP9) investigation is the most serious form of HMRC enquiry. It is used where HMRC suspects that a significant loss of tax has occurred as a result of deliberate conduct, that is, fraud.

Under COP9, HMRC makes an initial assessment of the suspected loss and invites the taxpayer to participate in the Contractual Disclosure Facility (CDF). Under the CDF, the taxpayer admits to deliberate conduct and makes a full disclosure of all tax irregularities. In return, HMRC agrees not to pursue a criminal prosecution.

If the taxpayer declines to participate in the CDF, HMRC may proceed to a criminal investigation. The stakes are therefore very high.

COP9 investigations typically involve:

• Large sums of unpaid tax, often hundreds of thousands of pounds.
• Multiple years under review.
• Complex financial affairs, offshore accounts or structures, or significant cash transactions.

If you receive a COP9 letter, you must seek specialist tax investigation advice immediately. This is not a situation in which general accountancy advice is sufficient, a specialist in tax fraud and COP9 investigations is required.

Do not respond to a COP9 letter without taking specialist legal and tax advice first. The decisions made in the early stages of a COP9 investigation can determine the outcome, and the consequences of a misstep can include criminal prosecution.

Yes. HMRC actively encourages voluntary disclosure of unpaid tax through a range of disclosure facilities, and the financial benefits of disclosing voluntarily, as opposed to waiting for HMRC to find the problem, are significant.

The main mechanisms for voluntary disclosure are:

• Online disclosure through the digital disclosure service. Suitable for straightforward cases involving undeclared income or incorrect returns across a limited number of years.
• The Worldwide Disclosure Facility. For offshore income and assets.
• The Contractual Disclosure Facility (CDF). For cases involving deliberate non-compliance, where full disclosure is offered in return for a commitment that HMRC will not pursue criminal prosecution.

The financial benefits of voluntary disclosure:

• Penalties are significantly lower for unprompted voluntary disclosure than for cases identified by HMRC. An unprompted disclosure of a careless error may attract no penalty at all.
• HMRC’s investigation time limit is shorter where the taxpayer has not been deliberately non-compliant.
• The process is more predictable and typically faster than a compliance investigation initiated by HMRC.

Voluntary disclosure is not an admission of fraud. For the majority of cases, it involves simply correcting errors or omissions in prior years’ returns, paying the tax due with interest, and moving forward with a clean compliance record.

If you are aware of an error or omission in any prior year’s tax return, speak to your accountant before HMRC contacts you. The difference in outcome between an unprompted voluntary disclosure and a case identified by HMRC can be very significant, in both financial and practical terms.

HMRC’s penalty regime is structured and graduated, with the level of penalty determined primarily by the behaviour that led to the error and the extent of co-operation during the investigation.

Penalty ranges:

• Reasonable care taken, no error: no penalty.
• Careless error, unprompted disclosure: 0% to 30%.
• Careless error, prompted disclosure: 15% to 30%.
• Deliberate error, unprompted disclosure: 20% to 70%.
• Deliberate error, prompted disclosure: 35% to 70%.
• Deliberate and concealed error, unprompted disclosure: 30% to 100%.
• Deliberate and concealed error, prompted disclosure: 50% to 100%.

Penalties are expressed as a percentage of the ‘potential lost revenue’, the additional tax that would have been payable if the return had been correct. A penalty of 50% on a liability of £50,000 is a penalty of £25,000.

In addition to these behaviour-based penalties:

• Interest accrues on all unpaid tax at HMRC’s current late payment rate (which significantly exceeds commercial savings rates).
• Surcharges may apply for late payment of VAT.
• Fixed penalties apply for late filing and late notification of registration obligations.

In the most serious cases involving deliberate fraud, HMRC can also pursue criminal prosecution, which carries the risk of fines and imprisonment.

Professional representation during an HMRC investigation almost always produces better outcomes than self-representation. An experienced tax adviser knows how to present information, negotiate with HMRC, reduce penalties through disclosure and co-operation, and challenge assessments that are excessive.