“They're coming in from the cold. They're nervous,” Edward Robbins, a criminal defence lawyer and former federal prosecutor in Beverly Hills, California, was quoted as saying.

The US government plans to prosecute US citizens for evading taxes on income generated through foreign accounts they failed to disclose on their tax returns, Mr Robbins said.

Swiss banks, by law, cannot disclose account holder information, but increasing pressure from the United States and members of the European Union is forcing Swiss banks to reconsider excessive secrecy, The Washington Post reported at the weekend.

Dozens of wealthy US citizens began contacting criminal tax lawyers after Bradley Birkenfeld, formerly employed by Swiss bank UBS, pleaded guilty last year to helping Igor Olenicoff, a California billionaire, conceal $200 million, said a US Senate report.

The report estimated off-shore tax havens cost the US about $100 billion annually.