The names of dozens of suspected fraudsters and tax evaders have cropped up in a stash of stolen Swiss bank data recently passed to Revenue & Customs, according to people familiar with the situation.

Accounts of about 3,000 British residents will be prised open using the cache of data allegedly stolen by an ex-employee of HSBC’s Swiss private bank.

A sample analysis suggests that as many as a fifth of the account holders have previously aroused the suspicions of tax inspectors for evasion or other offences including “missing trader” value-added-tax fraud, a multi-billion cross-border scam.

The possibility that a significant proportion of the recorded bank balances, which run into many hundreds of millions of pounds, are untaxed has raised hopes that investigations will yield a substantial windfall for the Treasury. Probes into a number of account holders are likely to be launched shortly.

HSBC acquired its Swiss private banking interests with the 1999 acquisition of the Republic banking group built up by Edmond Safra, the Syrian-born financier. It said this week: “HSBC does not condone tax evasion.”

The leak affecting 15,000 clients from around the world is one of a spate of data thefts that has rocked the world of private banking and put the long-standing Swiss tradition of banking secrecy under intense strain. This week, German prosecutors raided Credit Suisse offices in the latest stage of an investigation based on discs allegedly stolen from banks and offered to the authorities.

Tensions over the use of stolen data by foreign authorities to pursue tax evaders are running high in Switzerland, although governments have signalled that they obtained the HSBC data through legal means and without paying for it.

The list was allegedly stolen in 2006 and 2007 by Herve Falciani, a former IT employee who worked at HSBC’s offices in Geneva. The data fell into the hands of the French authorities last year when they searched his home in the South of France at the request of Swiss prosecutors after he absconded from Switzerland.

France has since passed it onto other governments, including Spain and the UK, following requests made under the terms of their double tax treaties. It is reported that Mr Falciani denies breaking any laws.

French officials passed the list to the UK’s Revenue & Customs about five weeks ago, after a delay caused by an unsuccessful application to the French courts by HSBC for a review of the law regarding information transfer. HSBC said: “We are doing all we can to protect the interests and confidentiality of our clients.”

The data in the hands of British authorities concerns accounts that are three to five years old. It lists a total of about 6,300 names but about half were advisers, family members or those with powers of attorney.

The data also contains names, addresses, details of advisers, transactions, account balances and information about the source of the funds, along with details of structures involving other jurisdictions such as the British Virgin and Cayman Islands. A sampling exercise involving about 200 accounts revealed that nearly 40 account ­holders had already come under scrutiny from tax inspectors.

The depth of information on transactions could put a spotlight on some wealthy foreigners living in Britain, even though they are entitled to have undeclared foreign accounts. Inspectors will be able to check whether the tax rules for “non-domiciled” residents transferring money in Britain have been met.

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