The board of Société Générale is set to call in independent auditors to examine the events leading up to the biggest rogue trading scandal in banking history, as directors on Tuesdday sought to bolster Daniel Bouton, chairman, ahead of a board meeting on Wednesday.

But the fate of Jean-Pierre Mustier, its star executive, hangs in the balance. The head of corporate and investment banking is to be grilled on what he knew of an alarm raised by Eurex, Europe’s leading derivatives exchange in November 2007. “Our previous assumptions have to be questioned,” said one director.