SAC Capital told its investors on Wednesday that it had been notified of possible enforcement action by the Securities and Exchange Commission. The hedge fund with $14bn under management held a 20-minute phone call with investors to tell them that it had been notified that the regulator intended to bring civil fraud charges â?? a procedure known as a Wells Notice.

US authorities say that SAC avoided losses of $194m and made $83m profit by betting against the share prices of pharmaceutical companies Wyeth and Elan ahead of the results of an Alzheimerâ??s drug trial.

Mathew Martoma, a former SAC portfolio manager, was arrested last week on insider trading charges.

SAC and Steven Cohen, the founder and head of SAC Capital, have not been accused of wrongdoing and the company has said it is co-operating with the inquiry. A lawyer for Mr Martoma has said that he will fight the charges and expects to be exonerated.