French socialist Benoit Hamon is expected to emerge as the French left’s presidential candidate as voters go to the polls amidst scandal on the right ahead of one of the country’s most unpredictable elections yet.

Party members voting in the second round of the Socialist Party’s primaries are making a choice between former education minister Mr Hamon and outgoing prime minister Manuel Valls.

The French election, which will take place on 23 April, has taken a surprise turn in recent weeks as the presidential favourite has become embroiled in a scandal over payments to his wife.

Right-wing candidate Francois Fillon is facing controversy as new allegations by French investigative website Mediapart and the Journal du Dimanche claim the former senator pocketed about €25,000 between 2005 and 2007 from a pot of money which provides allowance for assistants.

This comes after it was revealed by satirical newspaper Le Canard Enchaine that his Welsh wife Penelope Fillon received payments of €500,000 for work the paper claims she has never done.

Ms Fillon earned the money for her job as her husband’s assistant in parliament between May 2012 and December 2013 but the French newspaper found no traces or records of any of the work she carried out.

An investigation has now been opened by the French authorities over allegations of embezzlement of public money.

Three months ahead of the election, the scandal has damaged Mr Fillon’s campaign and raised questions over whether he should quit the presidential race.

The scandal has also opened the door for other candidates to prove their integrity ahead of the vote. French elections have rarely been so unpredictable.

An ultra-conservator and hard-liner, Mr Fillon has anti-abortion views, wants to axe corporation tax, deregulate the labour market and introduce tight immigration quotas.

But he has to deal with competition from the right in the form of the Front National’s Marine Le Pen, whose popularity has continued to surge despite her campaign still not having properly kicked off.

Polls are showing Ms Le Pen as winner of the first round with 26 per cent of the votes – going head to head with Mr Fillon in the second round with 25 per cent.

But the scandal over Ms Fillion’s payments has cost her husband his popularity as the latest poll by Odaxa shows he is 16 points down.

In addition, independent candidate Emmanuel Macron is well-placed to cause a surprise result.

The 39-year-old, who resigned from the Socialist government in August last year to launch his own movement En Marche! is trailing Ms Le Pen and Mr Fillon in the polls. And the gap is narrowing.

He is appealing to young generations from right and left because he appears not to have a defined place on the political spectrum, has never stood for elected office before and appears different from the old political class.

On the left, Benoit Hamon has gathered momentum that has given the Socialist Party a fresh look.

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Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-3 Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-4 SAN FRANCISCO, CA - JANUARY 28: Demonstrators hold signs during a rally against a ban on Muslim immigration at San Francisco International Airport on January 28, 2017 in San Francisco, California. President Donald Trump signed an executive order Friday that suspends entry of all refugees for 120 days, indefinitely suspends the entries of all Syrian refugees, as well as barring entries from seven predominantly Muslim countries from entering for 90 days. 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Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-9 NEW YORK, NY - JANUARY 28: Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. (Photo by Stephanie Keith/Getty Images) Getty Images Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-10 NEW YORK, NY - JANUARY 28: Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. (Photo by Stephanie Keith/Getty Images) Getty Images Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-11 NEW YORK, NY - JANUARY 28: Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-12 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-13 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-14 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-15 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-16 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-17 NEW YORK, NY - JANUARY 28: Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-18 Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-19 Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-20 Passengers wait in line to check in at the American Airlines terminal at JFK International Airport August 10, 2006 in the Queens borough of New York City. British authorities arrested 21 people and halted a anallegedly terrorist plot to use liquid explosives concealed in carry-on luggage to blow up airliners traveling between Britain and the U.S. Homeland Security chief Michael Chertoff said that the plot appeared to be directed at U.S. carriers flying out of Heathrow. such as United Airlines, American Airlines, Continental Airlines. Stephen Chernin/Getty

But the incumbent socialist President, Francois Hollande, remains deeply unpopular – with last year’s polls showing only 14 per cent of voters had a positive opinion of him – and this has badly affected people’s views of the left.

Mr Hamon resigned from his role as education minister in August 2014 because he believed Mr Hollande had abandoned his socialist agenda.

Mr Hamon, who has been compared to Bernie Sanders and Jeremy Corbyn, has a manifesto including plans for a universal monthly income for all citizens, legalising cannabis and backing investment in renewable energy.

On the other hand, free-market supporter Mr Valls is burdened by the government’s record.

Whether the payments scandal which stained Mr Fillon’s campaign will enable the left-wing candidate to win back enough votes to make it to the second round is unlikely, but not impossible.