A former French minister close to President Nicolas Sarkozy was in court Wednesday to testify -- and face possible charges -- in a probe into illegal campaign financing.

Eric Woerth was due to appear before investigating judges in the southwestern city of Bordeaux to give evidence in an inquiry into alleged illegal campaign financing by L'Oreal heiress Liliane Bettencourt.

A source close to the affair said Woerth could be charged with illegally raising campaign funds and taking advantage of Bettencourt, heiress to L'Oreal's immense cosmetics empire and France's richest woman.

Bettencourt is at the centre of a series of long-standing, overlapping legal inquiries, including one into claims she showered leading right-wing figures with envelopes stuffed with undeclared campaign donations.

Woerth, a former labour minister is suspected of having obtained illegal funds from Bettencourt to help finance Sarkozy's 2007 presidential election run.

Woerth and his lawyer, Jean-Yves Le Borgne, have refused to comment on the current inquiry.

Bettencourt's former accountant, Claire Thibout, has testified to having been asked a number of times in 2007 to provide batches of 150,000 euros ($197,000) to Woerth, then the treasurer of Sarkozy's UMP party.

Woerth left the government in 2010 and in 2011 police carried out searches of his home and the UMP's office in connection with the case.

Sarkozy, who is expected to run for a second term in April, has always strongly denied he or his campaigns took illegal cash.