Nicolas Sarkozy was questioned today by magistrates trying to establish whether he received illegal campaign funds from France's richest woman when he ran for president in 2007.

It was the first time since losing the presidency - and the legal immunity that went with it - in May that he has been questioned about the scandal which could poison any future comeback bid, something many conservatives are yearning for.

Hundreds of police officers stood guard as the 57-year-old arrived to face investigators for closed-door questioning at the Palais de Justice in the city of Bordeaux, southwest France.

In one strand of a broader inquiry, magistrates are looking at 4 million euros ($5 million) of cash withdrawals from the Swiss bank accounts of Liliane Bettencourt, heiress of the L'Oreal cosmetics empire.

Sarkozy denies any wrongdoing but any drawn-out legal probe may taint him with sucpicion that could damage his chances of running at the 2017 presidential election, which one recent poll showed 52 percent of his party's supporters want to see.

That is two to three times more support than is enjoyed by either of the two men fighting to succeed him, Francois Fillon and Jean-Francois Cope. An unseemly leadership squabble between those two has deepened ideological rifts inside the centre-right UMP party.

As part of the inquiry into financial relations with Bettencourt, police raided Sarkozy's Paris residence and offices in July.

Investigating magistrate Jean-Michel Gentil could decide, following his first question session, whether to put Sarkozy under full-blown judicial investigation.

Such investigations do not automatically lead to trial and often takes months or years to conclude.

Initial suspicions were fuelled three years ago when a woman who worked as an accountant for the mentally frail Bettencourt, now aged 90, alleged that a large cash withdrawal was earmarked for Sarkozy's campaign.

The Bettencourt affair is not the only cloud on the horizon.

Lawyers are also demanding that Sarkozy explain himself in two other cases, one concerning the terms of a submarine sale to Pakistan and another concerning lavish spending on opinion polls by his office when he was president.

Since his election defeat to left-winger Francois Hollande - which pushed the UMP into opposition after a decade in power - Sarkozy has followed the career path of other former leaders such as Bill Clinton and Tony Blair as a star conference speaker.