Some 6,000 account holders who bank with the Swiss branch of HSBC will have to answer to the British tax authority.
HM Revenue and Customs (HMRC) wants to verify that the account holders have declared all earnings. The potentially wayward taxpayers will get a warning letter offering them a last chance to get their affairs in order.
The HMRC said on Thursday that it had already started criminal and serious fraud probes into more than 500 individuals and groups.
“They will be offered a window of opportunity to contact HMRC and disclose all their tax liabilities,” the HMRC said. A source there told the Reuters news agency that account holders would have 30 days after being contacted to come forward.
The names of the account holders reportedly came from a disc stolen from HSBC’s Geneva office.
Britain and Switzerland signed a tax accord last week that would compel Swiss banks to pay backdated income on the long-standing accounts of British tax cheats.
If the parliaments of both countries agree, Switzerland will make an upfront payment of SFr500 million ($630 million) to cover retrospective payments at a rate of between 19 and 34 per cent. From 2013 onwards, a withholding tax of 27-48 per cent will be applied.
As a further concession to Britain, the Swiss authorities have agreed to provide assistance on up to 500 tax investigation requests per year.