A spokesman for HMRC was quoted as saying: “We are starting to send out letters to about 55,000 individuals in the UK. In the most serious cases, prosecution is likely to follow.”

WealthBriefing was unable to immediately confirm the details of the story.

The operation follows HMRC's legal victory last year that forced UK banking groups HBOS, Lloyds TSB, Barclays, HSBC and Royal Bank of Scotland to hand over details of more than 400,000 customers with offshore accounts. This was whittled down to 100,000 cases where the Revenue suspected that some UK tax was due.

Lloyds TSB, HBOS and RBS have subsequently received billions of pounds in UK public aid to recapitalise their business after the credit crunch. The part-nationalisation of the banks has raised fears about the confidentiality of client accounts, such as in the private banking segments of these banks.

Between April and July last year, 45,000 people came forward to give details of their non-UK savings, under the Offshore Disclosure Facility, which promised less harsh penalties for those who volunteered information. By agreeing to levy a penalty of only 10 per cent on top of the tax and interest due, HMRC succeeded in collecting £400 million.