UBS yesterday suffered its heaviest blow yet in the investigation into its offshore banking activities for rich American clients after US authorities said they had indicted Raoul Weil, the Swiss bank's head of global wealth management.

The US Department of Justice indictment also says other senior unnamed UBS executives were involved as alleged “co-conspirators”. “These executives occupied positions at the highest levels of management within the Swiss Bank, including positions on the committees that oversaw legal, compliance tax, risk and regulatory issues related to the United States cross-border business.”

Separately, the indictment includes detailed allegations about how other more junior managers regularly sought to circumvent US tax rules over a period of years.