France is preparing to impose punishing fines on banks that fail to monitor trading risks after a government report yesterday signalled serious weaknesses at Société Générale, which has been rocked by the biggest rogue trading scandal in financial history.

It also emerged yesterday that the losses notched up by SocGen, as it sought to close the €50bn (£38bn) in unhedged futures exposure built up by the alleged rogue trader Jérôme Kerviel, were far greater than the €4.9bn first announced by the bank.