Jerome Kerviel, the ex-Societe Generale trader who has more debt than anyone else in the world, has turned himself in to French authorities to begin a three-year jail sentence.

His return home is something of an end point to a saga that goes from huge unauthorised trades on the eve of the financial crisis, to a pilgrimage and papal meeting.

Back in 2008, Kerviel cost SocGen €4.9bn (£3.99bn) through unauthorised trading, in an episode which became one of the largest ever trading frauds.

The sharply-dressed Kerviel is, at least on one measure, the world’s poorest man, owing SocGen around $6.3bn (£3.7bn).

But consider that by this metric of net wealth, US medical students are among the worst off in the world while studying, yet are likely to earn much more that most upon qualifying.

Kerviel has spent the weekend hovering on the France-Italian border, refusing to cross into France unless he heard personally from President Francois Hollande.

The 37-year-old was eventually persuaded by prosecutors to enter the country, after they highlighted to him that his failure to oblige police would make him a fugitive.

He handed himself in at Menton police station late last night, flanked by swarm of reporters and supporters.

The former trader has always admitted making the unauthorised trades, but has argued that the bank turned a blind eye when they went well, but turned against him when they didn’t.

SocGen carried out an internal report that found managers at the bank had failed to follow up on tens of different alarms over Kerviel’s activities. A number of resignations followed, but no other charges were pressed.

In March, Kerviel was found guilty for a third time of placing €50bn worth of loss-making trades, with the courts rejecting his final appeal.

He’s spent the last three months on a self-styled pilgrimage from Vatican city, walking from Rome back to France, having met with Pope Francis in February.

Kerviel called the mammoth walk a personal and spiritual journey, where he continued crusading against the “tyranny” of financial markets.

“The fight will continue regardless of what happens”, he said yesterday, as he headed towards the French border, where he was ushered into a waiting police car.

A statement was issued by Elysee Palace on Saturday saying a formal request from Kerviel for a presidential pardon would be considered, but the latter spurned the option, saying asking for a pardon is admitting you’re guilty.

Meanwhile, French finance minister, Michael Sapin, said last night on LCI television: