Société Générale, the French bank at the centre of the world's biggest rogue trader scandal, today reported a 63 per cent fall in second-quarter profit as sub-prime-related losses at its investment banking division weighed on the results.

SocGen, France's second biggest bank, said net income fell to €644 million (£511 billion) in the second quarter from €1.74 billion in the corresponding period last year. Banking analysts had expected net income of about €520 million.

Shares in SocGen rose 6 per cent to €63.10 as the market believes the bank will not require a cash call to prop up a balance sheet weakened by the credit crunch.

The investment banking unit took a €1.2 billion loss directly relating to the credit crunch in the second quarter ended June 30.

Frederic Oudea, chief executive of SocGen, is also grappling with a record €4.9 billion trading loss from unauthorised bets by Jérôme Kerviel, a 31-year-old junior trader at the bank.

The securities unit posted a loss of €186 million in the three months on markdowns of credit derivatives and debt backed by bond insurers.

Kerviel was freed from prison in March after an appeal against his detention but he remains under formal investigation for breach of trust, computer abuse and falsification.

Yesterday, French authorities said a 24-year-old assistant of Kerviel had been placed under formal investigation. Thomas Mougard, a trading room assistant, was accused of "complicity in introducing fraudulent data into a computer system."

The losses from the Kerviel affair forced SocGen to raise €5.5 billion through a rights issue and led analysts to regard the bank as a takeover target.

BNP Paribas, France's biggest bank, considered bidding for SocGen this year but ultimately ruled it out.

Commenting on the outlook for the bank, Mr Oudea said today: “Société Générale will take advantage of the quality of its customer franchises, its solid capital position and the commitment of all its employees to pursue its strategy despite an environment that is likely to remain difficult.”

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