French Presidential Candidate Fillon and his wife faced intense questioning as polls favoured Le Pen
Last week, French police launched an investigation after Le Canard Enchain newspaper accused Penelope of being paid nearly £430,000 in eight years out of taxpayers coffers, despite claiming she did not "have a role" in her husband's office both last year and in 2008.
Mr Fillon said in a statement he and his wife provided information that would help “establish the truth on the work carried out by Mrs Fillon”.
The Thatcher-admirer has previously said he will abandon his presidential hopes if the police decide to launch a criminal investigation after this preliminary probe.
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Although these preliminary questions is not an indication of guilt, Fillon’s campaign seems to have been damaged already as the Kantar Sofres one-point poll revealed Le Pen is set receive more than a quarter of the vote.
Condemning the initial “misogynistic” article that claimed Penelope’s alleged fake job, Fillon said “the stink-bomb season has started”, in an attempt to ruin his campaign.
The 62-year-old’s lawyer Antonin Levy said investigators would be sent more evidence in the coming days to prove that Penelope Fillon's work was real and "very important."
Asked about what work Penelope Fillon, who had up until now said she was staying out of politics, Levy told BFM TV: "Working as a parliamentary assistant is not about writing up notes … and summaries, it is also sometimes less tangible, less concrete but as real.
"It's being the person one trusts.”
Welsh-born Penelope Fillon sitting next to her husband Francois
Analysts have said it could also make it harder for Fillon to stick to a platform of spending cuts and firing of civil servants.
Francois Miquet-Marty from the pollster Viavoice said: "This is harming him both in his bid to get to the Elysee (presidential palace) and also for his calls for the French to agree to tighten their belts for the sake of the recovery of the French economy.”
Penelope previously said in an interview, she had no invovlement in her husband's political roles
But despite being guaranteed a place in the second round of the election Le Pen is set to lose the presidential race to one of her two rivals, according to recent polls.
A privately organised Internet petition, asking Penelope Fillon to "give us back the 500,000 euros" had by Monday evening, has collected 248,000 signatures.