In the centre of Trappes, in Paris’s western suburbs, a group of young men are handing out flyers urging locals to vote for Benoît Hamon. Neither the name nor the face is familiar in Britain, but that could well be about to change today.

“Vote for this man and you will see the real France,” says one, thrusting a leaflet into my hand. It sounds more like a threat than a promise, but this rather gritty Parisian banlieue – the subject of several billion euros’ worth of regeneration investment – is Hamon’s home ground.

One of seven candidates in the first round of the Socialist party’s (PS) primary election to choose a presidential candidateon Sunday, Hamon, 49, was considered an outsider only a fortnight ago, but is fast gaining ground. To some, he is the French Bernie Sanders or Jeremy Corbyn – albeit a considerably younger version.

Hamon’s anti-capitalist programme includes a “universal wage” (a form of basic income), work sharing, the use of referendums to decide policy and the legalisation of cannabis. It has been dismissed as utopian by centrist critics, but that will not worry Hamon overly.

This is about the socialist movement showing that it can do populism and protectionism better than the far right.

France’s Front National leader, Marine Le Pen, is profiting from dissatisfaction among working-class voters who feel abandoned by both the left and the right. Hamon, his Socialist primary rival Arnaud Montebourg, 54, and the hard left presidential candidate Jean-Luc Mélenchon, 65, who is standing “outside the frame of political parties”, all argue that the Socialist party has abandoned the working class by shifting to the centre ground. This is embodied by Manuel Valls, the former prime minister and another primary contestant – who once reportedly suggested dropping the word “Socialist” from the party’s name.

Welcome to the French equivalent of the British battle for the heart and soul of the Labour party. “The others on the left are like Tony Blair but 20 years later,” said Ali Rabeh, Hamon’s chief adviser and a Trappes councillor. “But there is an international popular movement, with Jeremy Corbyn in the UK and Bernie Sanders in the US. People are looking for a popular left that is not centrist but offers something radically different.

“We feared that this election would be hijacked by the right and by issues like national identity and ridiculous arguments over things like the burkini. We felt it was absolutely important not to let that happen.”

Bruno Cautrès of Cevipof, the political research unit at Paris’s elite Sciences Po university, told the Observer: “François Hollande has disappointed many leftwing voters. Today, the left is divided between those who want to continue the same line as François Hollande and Manuel Valls, and those who say these are the very people who have created the economic situation we are in and we have to move to the left.

“The question arises of where is the line that marks the left these days. For many people who are asked, it’s the relationship with the working class, the poor and those with precarious jobs. But for a number of years now we have seen that it is Marine Le Pen who appeals to the working class.

“And in the PS primaries we are not seeing a lot of working-class issues being raised. Arnaud Montebourg and Benoît Hamon represent a left that is not just against austerity and deficits, but wants to reinvent the idea of the left by transforming society. It is different, but I don’t think this is particularly seductive to the working classes.”

Hamon’s team argue that as long as political parties on the centre-right and left keep throwing out the same ideas, which have done nothing to reduce unemployment and poverty in France, voters will continue to turn to the Front National. Hamon’s programme, they argue, is about thinking out of the box.

After the “champagne left” and the “caviar left”, Hamon is the “realistic left”, said Rabeh. “What is ‘utopian’ is people believing that ideas that have been shown not to work will somehow start to work. Benoît Hamon doesn’t have a miracle solution. He’s saying it’s not simple, but what the left and right have been doing hasn’t worked so let’s try something different, very different. What we are proposing is radical change. And I’m convinced that if this kind of left takes [control] of the PS we can halve the FN’s score.”

Laurent Bouvet, a professor at Versailles University, said that, although the new left surge was different, it was unlikely to be enough to lure the working class away from Le Pen.

“We are not seeing any significant working-class vote for the left, not even for Mélenchon, who is the furthest left. This category of voters will either abstain or will vote mostly for Marine Le Pen. There is no popular vote for the Socialist party.”

Bouvet described Hamon’s programme as an almost but not quite utopian, post-work, 19th-century idea of socialism. “That said,” he added, “it’s possible Hamon will have a good score. He may even head the first-round vote because his voters will mobilise. It will come down to participation. If we have two million-plus, Manuel Valls has a chance. If we have less than 1.5 million, Hamon could win.”

In Trappes, shopkeeper Karim Chrifi, 50, who has lived all his life in the town, said Hamon was popular because he was seen as “one of us”. “He isn’t like other politicians. He drives here in his small car, parks, has a coffee and talks to us. He touches on the real issues that concern us: poverty, work, wages, crime … If it weren’t for Benoît Hamon and Arnaud Montebourg, who else would we vote for? Marine Le Pen.”

Whatever the outcome of the vote, and the attempts by Hamon, Montebourg and Mélenchon to drag French socialism out of the centre ground, most believe the Socialist party candidate will be defeated in the spring presidential election. The current money is on a second-round run-off between Le Pen and the right-wing Les Républicains candidate François Fillon.

“The situation is very comparable to that in the UK,” Cautrès said. “The Labour party could have chosen a mainstream, some would say more realistic, candidate and instead it chose Corbyn. It could be that the PS will do the same. The left wing of the left could win the primaries, but it won’t win the presidential. That seems impossible.”

At his last rally last week, Hamon, a small figure in suit and tie, was greeted like a rock star by almost 4,000 mostly young people. They were chanting: “Benoît président.”