Switzerland threatened to seize the names of 52,000 Americans from UBS rather than allow the Swiss bank to hand over the data to the US tax authorities.

UBS faces a court hearing in Miami on Monday, where it is being sued by the Inland Revenue Service (IRS)

The IRS, which suspects the Swiss bank of helping wealthy Americans to hide almost $15 billion so they could avoid paying tax on the money, wants UBS to give it the names of about 52,000 clients with Swiss bank accounts.

UBS claimed that revealing its clients’ identities would force it to break strict Swiss banking secrecy laws.

The Swiss Justice Ministry warned today that it would take control of the information rather than allow UBS to give it to the IRS.

"Switzerland will use its legal authority to ensure that the bank cannot be pressured to transmit the information illegally, including if necessary by issuing an order taking effective control of the data at USB," the country said in a filing to the Miami court.

President Barack Obama has made fighting tax evasion one of his top priorities.

Switzerland has already made concessions on its famed banking secrecy, including agreeing a bilateral tax treaty with the US last month.

Under the new agreement, Switzerland would hand over information on bank customers if tax authorities can provide evidence that tax has been evaded. But it would not allow America to ask for the names of clients in the hope of finding evidence of tax evasion.

In February, UBS admitted that it helped some American customers avoid tax and agreed to pay a $780 million (£483 million) settlement. The bank also gave the IRS the names of 250 clients.

Hans-Rudolf Merz, Switzerland’s finance minister, has previously said that UBS could settle the latest civil case before it comes to trial on Monday.

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive