French investigators have raided the home and offices of former President Nicolas Sarkozy in connection with a probe into the alleged illegal financing of his successful 2007 presidential campaign.

The investigation concerns possible illegal contributions made to Sarkozy’s campaign by Lilliane Bettencourt, France's wealthiest woman and heiress to the L'Oreal cosmetics fortune.

Sarkozy, who lost the presidential elections to Francois Hollande in May, has long denied any impropriety.