Former French president Nicolas Sarkozy went before a judge today to respond to suspicions he illegally accepted donations from France's richest woman to fund his 2007 election campaign.

The judge in Bordeaux could decide whether the 57-year-old conservative, a polarizing figure who often faced criticism for cozy ties to the rich, will be charged with taking advantage of the 90-year-old L'Oreal heiress, Liliane Bettencourt.

Sarkozy has consistently denied all allegations.

Bettencourt's former accountant told police that she handed over $192,000 US in cash she was told would be passed on to Sarkozy's campaign treasurer. In July, a magistrate ordered the seizure of Sarkozy's diaries.

Though it pales in comparison to U.S. campaign funding amounts, the sum shocked many French citizens because spending on political campaigns is tightly limited. Individual campaign contributions to candidates are limited to just more than $5,900, and no candidate can spend more than $28.4 million on an entire presidential campaign. The French government reimburses some of that money to the winner.

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French police officers take their positions at one of the main entrances of the courthouse in Bordeaux, southwestern France, after former French president Nicolas Sarkozy arrived on Thursday. (Bob Edme/Associated Press)

By comparison, Barack Obama and Mitt Romney each raised and spent hundreds of millions of dollars in the campaign for this year's U.S. presidential elections.

"Given the extremely strict rules and controls, illegal financing is completely impossible," said Claude Gueant, who was Sarkozy's campaign director at the time, chief of staff and later his interior minister.

The probe centres on the finances of Bettencourt, the focus of a long-running family feud over her fortune that ballooned in 2010 into a multi-layered investigation and political affair. Bettencourt, reportedly suffering from Alzheimer's disease, has since been placed under legal protection.

Sarkozy lost his immunity from prosecution when he lost the presidency to Socialist François Hollande in May. Since then, his conservative UMP party has fallen into disarray. The former president's ties to the wealthy alienated many in France, but he remains popular among the country's conservatives despite the legal problems that have dogged him since leaving office.

Sarkozy entered the Bordeaux courthouse Thursday without notice after a decoy vehicle lured away the camera crews hoping to catch him on the way in, according to the Sipa news agency. He and his lawyer met privately with the judge who will decide whether he faces charges.