The former French president Nicolas Sarkozy has been placed under formal investigation, over claims his 2007 election campaign received illegal donations from France's richest woman.

Mr Sarkozy is accused of accepting thousands of euro from L'Oreal heiress Liliane Bettencourt.

The former leader denies taking financial advantage of Mrs Bettencourt.

His lawyer said he would file an appeal against what they described as the "incoherent and unfair decision".

It's alleged that staff acting for Mrs Bettencourt, who is 90 years old, gave 150,000 euro in cash to Mr Sarkozy's aides during his successful 2007 campaign to become president.

Police raided the ex-president's home and offices last July after he lost his immunity.

Mr Sarkozy has dismissed as mere "gossip" claims that he took envelopes stuffed with cash.