Nicolas Sarkozy

Former French president Nicolas Sarkozy is to face a probe over accusations he took illegal donations from a mentally frail Liliane Bettencourt to fund his election campaign in 2007, Bordeaux prosecutors have said.

After hours of face-to-face grilling of Sarkozy and several former members of L'Oreal heiress Bettencourt's staff, judge Jean-Michel Gentil opened a formal investigation into allegations that the former president tried to manipulate 90-year-old Bettencourt into giving donations for his 2007 election campaign.

In November, Sarkozy faced a similar 12-hour interrogation in which he claimed he had met Bettencourt only once, in 2007, and had never asked her for a "penny". The judges accepted his version and made him an "assisted witness" in the case.

But under Gentils' renewed questioning, four members of Bettencourt's staff alleged that Sarkozy had met her several times in 2007.

Now he has been formally accused of being a part of the scandal, placing him just one step short of a charge. The prosecutors have placed him under investigation for "taking advantage of a vulnerable person during 2007 to the detriment of Liliane Bettencourt".

Sarkozy, 57, will appeal against the "incoherent and unfair decision". He said he had forged a close relationship with Bettencourt during his time as the mayor of Neuilly-sur-Seine, the wealthiest suburb of Paris.

Bettencourt's former staff claimed Sarkozy's aides received €150,000 (£128,000) in cash during his 2007 campaign. In 2010, Bettencourt's former accountant, Claire Thibout, said Sarkozy's campaign manager at the time, Eric Woerth, who later went on to become the budget minister under Sarkozy, had collected the cash in person.

Woerth was forced to resign in July in the wake of the scandal. He is under formal investigation.

In France, the individual donation limit for election campaign is pegged at €4,600.

A charge of deliberate manipulation of a vulnerable person can carry a three-year jail sentence and €375,000 fine and disbarment from public office for five years - torpedoing his ambition of running for presidency again in 2017.

Sarkozy would be the second successive former president of France, after Jacques Chirac, to be accused of illegally funding his political career. Chirac was convicted in 2011 on corruption-related charges during his time as the mayor of Paris.