Hundreds of wealthy taxpayers have been sent letters by HM Revenue & Customs (HMRC) over possible large-scale tax evasion as part of an effort to clampdown on tax dodgers.
It is understood that most of the letters relate to offshore bank accounts held at HSBC in Switzerland after HMRC acquired a list of well-off individuals with accounts at the bank.
The letters sent out are known as Code of Practice 9 and advise the recipients that HMRC will investigate any situation of suspected serious tax fraud.
An HMRC spokesman said: "The days of hiding money offshore to evade tax are now over."
The news comes after the coalition Government announced a crackdown on tax avoidance.
Deputy Prime Minister Nick Clegg warned that the coalition would come down "as hard on tax cheats as on benefit cheats".
Tax evasion is estimated to cost the Treasury £7 billion each year in uncollected revenues, and avoidance the same again.
HMRC's accounts for 2009-10 stated that losses from written-off or remitted tax debt stood at £6.3 billion.
It was reported that HMRC was given the list of wealthy account holders by French prosecutors. It is understood the list was stolen by a former HSBC employee in Switzerland.
A spokesman for the bank said: "We do not condone tax evasion", but would not comment on the incident.
