Two bankers, including a former employee of UBS, the world’s leading wealth manager, have been charged by US authorities with helping a American billionaire evade income taxes on about $200m of assets deposited in Swiss and Liechtenstein bank accounts.

Bradley Birkenfeld, Mario Staggl and “others known and unknown” were accused in the indictment, unsealed on Tuesday, of conspiring to defraud the US from at least 2001 by engaging in a scheme that included falsifying documents, helping to set up shell companies and destroying banking records.