The UK government is to acquire the Swiss bank account details of up to 6,600 wealthy UK citizens suspected of evading tax after information was stolen from HSBC’s private bank in Switzerland by a software engineer, the Sunday Times (of London) reported.

The report comes shortly after it was reported that the Swiss authorities are to investigate the matter. HSBC’s private bank has apologised to clients about the theft, which affected a total of 24,000 accounts, of which 15,000 were in use at the time of the theft about three years ago.

HSBC told WealthBriefing that it has fewer than 6,000 UK clients of its Swiss private bank - a figure which is at odds with the newspaper's report. The bank said it was unable to make further comment at this stage.

The UK tax authority declined to comment on the matter.

HM Revenue & Customs expects to benefit from the exploits of Hervé Falciani, a French software engineer, the newspaper said.

The issue not only demonstrates how ruthless governments are prepared to be when it comes to fighting tax evasion, but also how client secrecy has been compromised - not only by governments, but by bank employees who, seeing governments’ desire for this information, increasingly see it as a way of profiting. The matter also raises questions of whether governments, many of which have big budget deficits, are abusing basic principles of law in their desperation for revenue.

The French government has tried to use the data, triggering a diplomatic row with Switzerland. The Swiss authorities have made it clear they will not support the use of the stolen data to answer requests from foreign authorities, while the French authorities have informed the Swiss authorities that the data they hold will not be used “inappropriately”, HSBC said in a statement.

When the French government was approached with a possible sale of the data, the affair led to a diplomatic row with Switzerland and the latter nation threatened to cease co-operation on tax issues. 

Meanwhile, a senior UK tax official was quoted by the newspaper as saying: “We expect to have this information soon - perhaps within a week. I would certainly expect within a month.”

“It’s fair to say that the prospect of getting hold of this information has generated some excitement here,” the official said.

Switzerland, which prides itself on the secrecy of its banking system, has long been a popular haven for rich Britons eager to keep their wealth out of reach of the taxman.

Mr Falciani’s theft is on a far larger scale than that from LGT, the Liechtenstein private bank. The UK’s tax authorities had paid Heinrich Kieber about £100,000 ($151,766) for details of some 300 UK customers of LGT where he, too, had worked in the IT department.

It is understood that HMRC raised more than £100 million by using the data.