Jean-Pierre Mustier, the former head of investment banking and head of asset management at Société Générale, and Robert Day, a non-executive director, are being probed by the French regulator for alleged insider trading, the bank has announced. It said that Mustier, who had been due to quit SG by the end of the year, has resigned with immediate effect in view of the move.

The bank said in a press release this afternoon that it had received a letter from the French Financial Markets Authority (AMF) about an investigation the Authority opened in January 2008 into the financial information and market of Société Générale shares. The investigation came in the same month that the bank discovered a rogue trading scandal that cost it €4.9bn ($6.3bn).