The US crackdown on clients of UBS is widening into a global hunt, with the government detailing in court documents how the Swiss bank and outside advisers helped Americans hide money using enterprises set up in Hong Kong.

For the first time in the government's long-running bid to ferret out the names of US tax-evaders from the Swiss bank's client list, plea agreements entered in the case are providing a clearer picture of UBS's sophisticated efforts to help Americans hide income or the existence of foreign bank accounts.