Jérôme Kerviel, the rogue trader, was today brought face to face with the assistant who he says helped him to cover up the illegal deals, which led to losses of €4.9 billion (£3.9 billion) at Société Générale, the French bank.

The encounter was organised by investigating magistrates seeking to determine whether the 31-year-old trader acted alone when he made his ultimately disastrous trades on European stock markets by using a technique known as a "martingale", where bets are doubled on every loss.

Mr Kerviel, who has been placed under investigation on suspicion of breach of trust, fabricating documents and illegally accessing computers, claims other employees, including Thomas Mougard, his assistant, knew of his unauthorised transactions.

Mr Mougard, who is accused of "complicity in introducing fraudulent data into a computer system", denies the claims.

Investigators said the confrontation would help them establish who was telling the truth.

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