A former colleague of the senior UBS banker detained by US authorities last week has been charged over allegations he helped a billionaire real estate developer evade millions of dollars in US income taxes.

Bradley Birkenfeld, 43, formerly a director in UBS’ wealth management division, was charged with a single count of conspiring to defraud the US.

While at UBS, Mr Birkenfield worked in a team led by Martin Liechti, the senior UBS banker who was arrested last week by US prosecutors investigating tax irregularities at the giant Swiss bank. Mr Liechti, who was detained as a material witness, was released without charge.

Mr Birkenfeld’s indictment also names Mario Staggi, 43, a Liechtenstein-based banker.

Prosecutors accuse the pair of fictitious trusts, bogus companies and other false entities to hide around $200 million in assets for an unnamed US client. They each face up to five years in prison if convicted.

The indictment is part of a wider investigation by the US Department of Justice examining whether UBS bankers helped a series of clients evade US taxes.

UBS said it was co-operating with the investigation but declined to comment on the indictment of a former employee.

The Securities and Exchange Commission, the US regulator, is also investigating whether the bank broke registration rules.

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