German tax authorities have purchased confidential information about clients of Coutts, the UK bank, to see if they were hiding money in Switzerland, according to media reports over the weekend.

Financial Times Deutschland and Der Spiegel, citing unnamed sources, said officials in North Rhine-Westphalia paid €3.5 million (around $4.26 million) for a compact disc containing the names of 1,000 rich Germans who had accounts with Coutts in Zurich.

"We are aware of the continued media speculation regarding a potential breach of client data secrecy at Coutts. Following a thorough investigation, we have no evidence to suggest any such breach has taken place. As we stated to media last year, we take the protection of client data extremely seriously," Coutts told WealthBriefing in a statement today.

One media report said that tax authorities in North Rhine-Westphalia did not respond to emails and calls for confirmation.

In the past, the state has bought other CDs containing client names of Swiss-based banks. The purchases have been followed by tax investigations against hundreds of German taxpayers.

The use of stolen information, as well as irritating Swiss authorities, also highlights how determined some public bodies are in hunting for potential revenues. It also raises issues of whether, in their determination to find tax dodgers, the authorities are abusing principles of due process of law. The theft of bank CDs also raises question marks about the security of such data in the first place.

Germany and Switzerland have agreed on an account disclosure deal under which people with hitherto undisclosed Swiss accounts come clean in return for a payment. The UK has also reached a similar account disclosure deal with Switzerland.

Although Germany's double-tax treaty with Switzerland has not yet been confirmed, it would appear that a purchase by Germany of stolen data would breach such a treaty, casting doubt on whether such a purchase might have taken place, this publication understands.