The conservative is alleged to have paid hundreds of thousands of euros in taxpayers' money to his British wife Penelope for work she may not have carried out.

Two of the couple's children, Marie and Charles, have also been interviewed by investigators over claims they held "fake jobs".

"He was charged this morning. The hearing was brought forward so that it could take place in a calm manner," his lawyer Antonin Levy told AFP.

"Never been the assistant"

Last month, controversy surrounding his wife's official employment deepened with the emergence of a 2007 video interview. 

French investigative TV show Envoyé Special obtained a copy of an interview that Francois Fillon's wife Penelope gave to The Daily Telegraph in 2007, in which she says she has "never been the assistant" of her husband.

The interview with Mrs Fillon was conducted in 2007 when Mr Fillon was appointed French prime minister by Nicolas Sarkozy, who was president at the time.

Le Canard Enchaine, a French satirical magazine, reported that Mrs Fillon was paid from state funds between 1998 and 2013 for working as a parliamentary assistant, despite finding no evidence of any work having been done.

The couple have insisted that the salary was above board because she had worked for him from home.

"She corrected my speeches, she received countless guests, she represented me in protests, she passed on people's requests … she did it willingly for years," Mr Fillon said in his wife's defence.

Under French law, family members are permitted to work for parliamentarians.

'Anti-Semetic overtones'

It hasn't been a good week overall for Fillon - his party faced fresh controversy this week after his party tweeted a caricature with anti-Semitic overtones and a newspaper claimed a mystery benefactor bought him luxury suits.

His party, Les Republicains, has said it is launching an investigation after a tweet showed rival Emmanuel Macron with a suit, top hat and hooked nose.

The tweet first went out on Friday, with the party later posting a revised version showing a photo of Mr Macron instead.

Mr Fillon called it "unacceptable" and said he could not "tolerate the party spreading caricatures that use the codes of anti-Semitic propaganda".

Election

The French presidential vote will follow a 'two round' process. The first vote will take place on April 23rd. This will see the full field of candidates narrowed down to two, who will both progress to a run-off election on May 7th.

Fillon is up against far-right Marine Le Pen, centrist Emmanuel Macron and left-leaning Benoît Hamon & Jean-luc Melenchon respectively.