French former prime minister Francois Fillon has said allegations his wife was paid for a fake job were attempts to harm his presidential bid, adding that they only strengthened his resolve to run in the election.

Satirical weekly Le Canard Enchaine reported yesterday that Penelope Fillon had been paid some €600,000for many years of employment as a parliamentary assistant to Mr Fillon, then to his replacement as a lawmaker and also for work at a cultural journal.

The newspaper said its research had showed there was no evidence she had ever really worked. Mr Fillon, a 62-year old conservative, said that was not true.

His wife, he said, did work that included press reviews, proof-reading his speeches and meeting people for him.

"My wife has been working for me forever, ever since I first got elected in 1981," Mr Fillon told TF1 television, adding that she did it for free for a long time before he hired her in 1997 as a parliamentary assistant.

"The question is why - while my wife had been paid from1997 - this comes out now, two and a half months before the election? Clearly this is to try and take me down as a presidential candidate."

Mr Fillon, the conservative frontrunner in this spring's election, had seen his ratings drop slightly in recent weeks prior to these allegations and had been looking to a big rally in Paris on Sunday to inject fresh life into his campaign.

But the allegations about his wife Penelope have rattled the campaign of a man who has pitched himself to voters as an honest and morally irreproachable candidate, worrying lawmakers in his The Republicans (LR) party.

"We're in trouble, this is really not helping us," one LR lawmaker said earlier today on condition of anonymity.

Mr Fillon had until now been seen on a fairly smooth trajectory towards the Elysee - the election will be held in two stages, on 23 April and 7 May - despite a strong challenge from far-right party leader Marine Le Pen and from centrist Emmanuel Macron.

The image conveyed by the Welsh-born Penelope Fillon's own rare public comments and glossy magazines is of a woman leading a country life and keeping home for her family in their 12th century chateau near Le Mans, west of Paris.

Last October she told a newspaper, Le Bien Public: "Up to now, I have never been involved in the political life of my husband."

Mr Fillon, saying the allegations that his wife did not do real work were "abject", added that she meant she was not involved in politics.

He also revealed that two of his children, who are lawyers, did paid work for him at some point when he was senator.

It is not illegal for French parliamentarians to employ wives or children, but it would be illegal to use the money lawmakers get to pay assistants for someone who does no work.

A lawyer for Mr Fillon went to the financial prosecutor's office today to present evidence, after prosecutors opened an inquiry the day before for misuse of public funds following the story.

The opening of a preliminary investigation is a first step in the judicial process and does not mean that either Mr Fillon or his wife will eventually be charged or even placed under formal investigation.