The junior trader who left Société Générale battling to retain its independence after he lost €4.9 billion (£3.7 billion) was taken into custody last night after a French court was told that he could tamper with evidence if he were allowed to walk free.

Jérôme Kerviel, 31, was remanded in jail by the Paris Appeal Court after prosecutors challenged a decision to grant him bail. The hearing came as the inquiry into the scandal broadened. An employee of Newedge, a firm of brokers owned in part by Société Générale, was questioned by French police after they discovered an e-mail from him to Mr Kerviel that read: “You haven’t done anything illegal in terms of the law.”

Moussa Bakir, 32, was taken into custody on Thursday and detained overnight. Communications between Mr Bakir and Mr Kerviel were uncovered by SocGen’s own investigators and passed on to detectives this week.

The Société Générale trader is under investigation after it emerged that he had taken unauthorised bets totalling €50 billion on a falling stock market.

The biggest rogue trading scandal in history has plunged the bank into crisis, forcing Daniel Bouton, its embattled chairman, to seek a €5.5 billion capital increase as he strives to fend off takeover bids.

Mr Kerviel, who is accused of falsifying documents to cover his positions, faces charges of forgery, breach of trust and tampering with an IT system.

The bank also handed over to investigators Mr Kerviel’s mobile telephone bills, which are understood to have amounted to about €1,000 a month. The bank had backed Mr Kerviel’s assertion that he had acted alone. Yesterday, however, it appeared to change its stance after the detention of Mr Bakir.

“The inquiry seems to be at a turning point,” Jean Veil, a Société Générale lawyer, said. Mr Bakir worked for Fimat, SocGen’s wholly owned broking business, which merged with Calyon Financial, a division of Crédit Agricole, to form Newedge in January.

According to Société Générale, Mr Kerviel often used Fimat to process his trades, some of which were cleared by the broker’s office in London.

A source at the bank said that managers “could not understand” why Fimat had failed to alert the group to the extent of the trader’s dealing. Fimat’s offices were searched by police on Thursday, a judicial source said.

The legal moves continue apace with the board of Société Générale expected to meet this weekend to finalise its rights issue, which could be initiated next week.

A takeover battle for the bank is expected to break out after the capital increase, with BNP Paribas, its large domestic rival, likely to be in pole position to acquire SocGen.

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