What is a tax investigation by HMRC?
Answered 17 March 2026
Based on the retrieved sources, here is a comprehensive answer:
What is a Tax Investigation by HMRC?
HMRC Guidance / Practice
Definition
A tax investigation by HMRC is formally referred to as a compliance check (sometimes known as a "tax enquiry"). It is when HMRC checks your tax position. HMRC carries out compliance checks to:
- make sure you're paying the right amount of tax at the right time
- make sure you're getting the right allowances and tax reliefs
- discourage tax evasion
- make sure the tax system is operating fairly
More technically, the word "investigation" (as used in HMRC's compliance manuals) carries its ordinary meaning of "a systematic or formal inquiry to establish the truth" or "a careful search or examination in order to discover facts." An investigation involves gathering information to show:
- whether the person has committed a default,
- the extent and nature of any default, and
- what the penalty for any default is
How it works
HMRC will call or write to you to tell you what they want to check and why, and will also write to your authorised tax agent if you have one. You should continue to file your tax returns and pay any taxes due while a check is in progress. If you think HMRC should stop the check, you can write to them to explain why.
Types of Investigation
HMRC investigations can be civil or criminal in nature:
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Civil investigations – It is HMRC's policy to deal with fraud using civil investigation procedures wherever possible. In serious fraud cases, HMRC may use Code of Practice 9 (COP9), which gives the recipient the opportunity to make a complete and accurate disclosure of all deliberate and non-deliberate conduct that has led to irregularities in their tax affairs.
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Criminal investigations – HMRC may conduct a criminal investigation where they need to send a strong deterrent message or where the conduct involved means that only a criminal charge is suitable. HMRC reserves complete discretion to pursue a criminal investigation with a view to prosecution where it considers it necessary and appropriate.
In summary, a tax investigation by HMRC is a formal process by which HMRC examines a taxpayer's affairs to verify that the correct amount of tax has been paid. It can range from a routine compliance check to a serious fraud investigation, depending on the circumstances.
Citation sources
It’s HMRC policy to deal with fraud using civil investigation procedures, wherever we can. However, we can also conduct a criminal investigation. We might do this if: we need to send a strong deterrent message the conduct involved means that only a criminal charge is suitable
The HMRC Investigation of Fraud Statement The Commissioners of HMRC reserve complete discretion to pursue a criminal investigation with a view to prosecution where they consider it necessary and appropriate. In cases where a criminal investigation is not started, the Commissioners may decide to investigate using the Code of Practice 9 (COP9) investigation of fraud procedure. Under the investigation of fraud procedure, the recipient of COP9 is given the opportunity to make a complete and accurate
A compliance check (sometimes known as a ‘tax enquiry’) is when HMRC checks your tax position. We carry out compliance checks to: make sure you’re paying the right amount of tax at the right time make sure you’re getting the right allowances and tax reliefs discourage tax evasion make sure the tax system is operating fairly You can read this guidance to get help and support during the compliance check process. You can also get help and support using our online tool.
We’ll call or write to you to tell you what we want to check and why. We’ll also write to your authorised tax agent, if you have one. If we’ve started a check, you should continue to file your tax returns and pay any taxes due. If you need to speak to us about your compliance check, contact the officer who’s dealing with your case. Their details will be on the letter we sent you about the check. If you think we should stop the check, write to us to tell us why.
FA09/S94 does not define the word investigation. Its ordinary meaning is ‘a systematic or formal inquiry to establish the truth’ or ‘a careful search or examination in order to discover facts’. An investigation involves gathering information to show whether the person has committed a default, the extent and nature of any default, and what the penalty for any default is. For PDDD purposes, an investigation includes any compliance check. A compliance check is any action taken by an officer of HMRC