In September UBS revealed that it had discovered a potential loss of $2.3 billion thanks to unauthorised trading by a London-based employee at its investment bank.

The UK's Financial Services Authority and the Swiss Financial Market Supervisory Authority (Finma) immediately announced an independent investigation into the matter.

The FSA now says it has commenced a formal enforcement investigation against UBS and is in close contact with Finma which has begun its own enforcement action.

Says a statement from the latter: "Finma will assess and rule upon the adequacy of the controls that were in place to prevent and detect unauthorised trading within the Investment Bank and their compliance with the Banking Act and the Stock Exchanges and Securities Trading Act and related regulations."

Meanwhile, the trader accused of making the loss, Kweku Adoboli, was today refused bail by a London court having earlier this week pleaded not guilty to charges of fraud and false accounting. The trial date is set for September.