UBS was sued yesterday by a former top private-banking client, Igor Olenicoff, as a US federal investigation into the Swiss bank’s offshore services continued, according to the New York Times.

Mr Olenicoff, a billionaire property developer, filed his complaint against UBS and nearly a dozen current and former executives of the bank in federal court in Santa Ana, California.

The lawsuit accuses UBS, another Swiss firm and two private businesses based in Liechtenstein and their employees of luring Mr Olenicoff into becoming a client and a participant in a deceptive investment scheme intended to evade US taxes.

The civil case is thought to be the first to be filed by a wealthy US client of UBS, which is under investigation by the Justice Department over whether it allowed its customers to evade US taxes by hiding money offshore, the newspaper said.

The case is also notable because it contends that Mr Olenicoff’s former senior private banker, Bradley Birkenfeld, received a large settlement from UBS after complaining that it had encouraged its private bankers to violate US tax laws.

The suit contends that UBS turned over Mr Olenicoff’s name to the US Inland Revenue Service in about 2005, a move that would have been surprising for a Swiss bank that follows the tradition of banking secrecy. Mr Olenicoff is accusing the defendants of fraud and breach of fiduciary duty, among other issues.

UBS said it had not seen the complaint and thus could not comment upon it.

Mr Olenicoff has already run foul of the US tax code. In December, he pleaded guilty to criminal charges of tax evasion and lying on his tax returns, all in connection with his offshore private banking accounts. He agreed to pay $52 million in back taxes.

Mr Birkenfeld pleaded guilty in June to charges of conspiracy and tax evasion, and agreed to cooperate with the investigation into UBS.