Lawyers for former UBS private banker Bradley Birkenfeld have asked for a review of the handling of the case against him for aiding wealthy Americans evade taxes.

Birkenfeld, who was sentenced to 40 months in prison in August, is due to go behind bars on Friday.

His lawyers have complained that federal prosecutors made “inaccurate, misleading and incomplete statements” to the judge who handed down the sentence.

Birkenfeld asked for an internal probe in a letter to United States Attorney General Eric Holder and the Justice Department’s Office of Professional Responsibility, which investigates allegations of misconduct.

“It is one thing to hold Mr Birkenfeld accountable for wrongdoing,” Birkenfeld’s lawyers wrote.

“It is another thing altogether to imprison Mr Birkenfeld on false information, especially when he is treated far more harshly than the wrongdoers who actually profited from the illegal tax schemes that Mr Birkenfeld disclosed.”

Before being sentenced, Birkenfeld cooperated with the Justice Department, US Senate and the Internal Revenue Service investigations of Swiss bank UBS.

The bank paid $780 million (SFr806 million) in February and handed over data on 250 accounts to avoid prosecution. It agreed to hand over details of another 4,450 clients sought by the IRS.

At Birkenfeld’s sentencing in Florida, Justice Department prosecutor Kevin Downing said that the US could not have unraveled the bank’s “massive tax fraud scheme” without his cooperation.

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