Alleged rogue trader Jerome Kerviel went on trial in Paris yesterday accused of unauthorised deals that cost French bank Societe Generale five billion euros.

Dressed in a dark suit and purple tie, the 33-year-old replied "single, computer consultant" and declared a monthly salary of €2,300 when asked about his marital status and current occupation as the three-week trial opened.

The Frenchman is accused of gambling away €4.9 billion in risky stock market trades and of hiding these actions from his employers at Societe Generale.

The court must decide whether he is solely responsible for the losses in a case seen as a symbol of the banking excesses blamed for the financial crisis.

Branded a crook by his ex-employer but seen by others as a scapegoat for those higher up, Mr Kerviel faces criminal charges along with civil suits by the bank and other plaintiffs, including employees and shareholders.

He risks a maximum sentence of five years in prison and a fine of €375,000 if convicted on charges of breach of trust, falsifying and using fake documents and entering false data into company computers.

Societe Generale revealed in January 2008 that it had been forced to unwind €50 billion of unauthorised deals it says Mr Kerviel made.

He denies being solely responsible and has said he will call on the judge to acquit him when he takes to the dock at the Palais de Justice criminal courts in central Paris after a two-year inquiry.

Mr Kerviel has said he made mistakes but maintains his bosses knew what he was doing and that he was part of a "big banking orgy," as he described it in a memoir published last month.

He wrote that traders habitually hid the size of their bets and bosses turned a blind eye to possible breaches of trading limits as long as earnings were high.

Top earners received congratulations as "good hookers", Mr Kerviel wrote.

Mr Kerviel said last month that the trial was a chance "to show the public that I was not an isolated case and there were abuses throughout the banking and trading world."

He said that among the 33 defence witnesses at his trial, some would shed light on the workings of the trading floor to prove that he had not acted without his bosses' knowledge.

"My aim is to show that at no point did Jerome Kerviel abuse the confidence of the bank," said his lawyer Olivier Metzner ahead of the trial, vowing to present evidence recovered from trading computers to prove that Societe Generale was aware of Mr Kerviel's actions.

The bank's lawyer Jean Veil on the other hand has accused Mr Kerviel of "duplicity" for reassuring his employers that all was well.

"These hearings are going to open in a particularly tense atmosphere," Mr Metzner said.

Mr Kerviel spent 38 days in custody after his arrest in 2008 and has since started a job at a small IT company in a suburb of Paris.