The Queen's bankers Coutts have been forced to issue a statement denying that the confidentiality of hundreds of wealthy European customers has been put at risk.
It has been claimed that officials in the western German state of North Rhine-Westphalia paid £2.75m for a CD containing the names of 1,000 rich German clients of the private UK bank's Swiss unit.
Royal Bank of Scotland (LSE: RBS.L - news) -owned Coutts, which has served as banker to the British Royal Family since the 18th century, said it had no evidence that client confidentiality had been compromised.
In response to a report in the Financial Times Deutschland, a spokeswoman said: "We are aware of the continued media speculation regarding a potential breach of client data secrecy at Coutts.
"Following 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."
Germany has irritated Switzerland by repeatedly buying stolen bank data in its pursuit of suspected German tax evaders.
A deal between the two countries to end the tax row is being blocked by opposition-controlled German states such as North Rhine-Westphalia.
Earlier this year, Coutts was fined £8.75m by the banking watchdog over its anti-money laundering controls.
It received the fine from the Financial Services Authority (FSA) after a probe into its management of high-risk money laundering situations.
Tracey McDermott, acting director of enforcement and financial crime at the FSA, said at the time that Coutts' failings had been "significant, widespread and unacceptable".