HMRC can start a criminal investigation in various ways.
It may be alerted to an incidence of alleged fraud by another law enforcement agency. Investigations are sometimes prompted by HMRC’s own compliance checks and analysis of tax returns. Investigations sometimes start with whistleblower allegations or HMRC may respond to pressure generated by a media campaign.
Once it has decided to investigate, HMRC can apply for production orders under either the Police and Criminal Evidence Act (PACE) or the Proceeds of Crime Act (POCA).
Production orders are often a key building block in an HMRC investigation. They require the recipient to comply in providing HMRC with material including documents, digital material and accounting records. Failing to adhere to a production order is a criminal offence.
In the most serious cases, HMRC can apply to use intrusive surveillance powers under either the Regulation of Investigatory Powers Act or the Police Act. Investigatory techniques available to HMRC including bugging and covert filming / recording. The agency can also request data from telephone operators including records of calls made and messages sent; these activities are tightly regulated.
It is often the case that the subject of a tax investigation will know nothing of all this until HMRC makes it clear, either by executing a search warrant, conducting an arrest, or sending a formal letter of notice.
In most cases, the subject of HMRC’s tax inquiries will be invited for interview under caution, after which they are usually released while the investigation continues until a decision whether to charge is made by the CPS.