The US on Thursday indicted a former senior UBS banker and a Swiss lawyer for allegedly helping wealthy Americans hide assets in secret accounts, as Washington broadened its crackdown on offshore tax evasion.

The charges come a day after the US signed a deal with Switzerland giving it access to the names of 4,450 American clients holding offshore accounts at UBS, the country’s biggest bank, and signalled its intent to pursue tax evaders and anyone who may be helping them.