The controversy surrounding the British wife of France's centre-right presidential candidate has deepened with the emergence of a 2007 video interview aired last night on French television. 

French investigative TV show Envoyé Special has 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.

Over the past week, Mr Fillon, a former French prime minister and favourite to become president, has been fighting for his political career after reports claimed that his wife had been paid €831,400 of public money as his parliamentary assistant despite having no parliamentary pass or work email.

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.

However, in the newly emerged video, she states that she "had never been his assistant or anything like that".

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.

The couple have yet to respond to the latest twist in a scandal that threatens to change the course of the most crucial French presidential campaign in decades.

Back in November, Mr Fillon's win at the centre-right Republican Party primaries had been a genuine shock.

As the so-called "third man", Mr Fillon knocked out Nicholas Sarkozy in the first round and Alain Juppe in the second.

Election

The Fillon scandal, and a shock on the left of French politics, has turned this election campaign into an extraordinary and polarised contest.

Just a few weeks ago, it was assumed that the two centrist parties in France, the Republicans and the Socialists, would head into the elections with establishment personalities - both former prime ministers.

Manuel Valls was the assumed centre-left candidate for the ruling Socialist party, with Mr Fillon the centre-right choice for Les Republicains.

But last weekend, Mr Valls lost to Benoit Hamon - a candidate far to the left.

With Mr Fillon now in serious trouble, the only other option on the right is the Front National's eurosceptic, nationalist and populist candidate Marine Le Pen.

Polls say she will win the first round of the presidential vote, but with a ceiling of support thought to be around 25% nationally, she's not likely to win the second round run-off to become president.

That leaves independent candidate Emmanuel Macron as a genuine possibility for the presidency.

The 39-year-old former Socialist economy minister, who is pro-EU, was an outsider. But he is scandal free, he's ditched the establishment and he's attracting support from the centre-left.

Now, with Mr Fillon struggling, Mr Macron is gaining support from the right, too - meaning he could well be the man to beat.

The investigation into the Fillons' alleged financial impropriety is expected to take at least a month and is now understood to include work alleged to have been carried out by the couple's children.

Marie and Charles Fillon are said to have been employed as lawyers for their father despite not having law qualifications.