Outside Mantes-la-Ville’s 19th-century town hall stand two tall flagpoles with vast French tricolours flapping in the breeze. One of these used to be the European Union’s circle of gold stars on blue. But when a far-right mayor from the anti-immigration, anti-EU Front National was elected here, one of his first symbolic gestures was to pull down the European flag.

Mantes-la-Ville, 30 miles west of Paris, is the first town to be run by the Front National in the Île-de-France region that surrounds the capital. The mayor – Cyril Nauth, a 34-year-old high school history and geography teacher – won by just 61 votes in 2014 after a campaign centred on opposing the installation of a Muslim prayer room and a local mosque. His victory showed how the far-right party is expanding beyond its traditional heartlands on the French Riviera or in the de-industrialised former coal-mining areas in the north.



The horrific Bastille Day attack on Nice, in which a Tunisian delivery driver killed 84 people when he drove a heavy lorry at full-speed into a crowd watching fireworks, will be a defining concern in next year’s presidential and parliamentary elections. The Front National, which has accused the political class of failing to protect France, has already seen an increase in membership applications since the attack. Its key issues of security, immigration and national identity will dominate the debate.

A woman stands by a makeshift shrine to victims of the Nice truck attack. Photograph: Valery Hache/AFP/Getty Images

But Brexit — which has provided the Front National’s leader, Marine Le Pen, with a public relations boost and comforted her anti-EU stance — will also play a role in the party’s manifesto and it has sought to capitalise on it.



“Brexit is undeniably a historic moment,” Nauth told the Guardian. “It will change the general state of mind … French ruling parties, whether Les Républicains or the Socialists, have claimed for years that the European Union construction was absolutely unavoidable – we could do nothing against it and we could never leave. And yet the British, thanks to the very courageous vote of their people, have now totally demolished that theory.”



The fact that immigration was one of British leave voters’ key concerns has particularly interested the party. “Immigration is one of the most important political issues at the start of the 21st century,” Nauth said. “Little by little, the ideas of patriotism and sovereignty are growing with each election [in Europe], that is very encouraging for us in France and for the Front National.”



The British , European and French flags in Amiens prefecture, northern France, during a visit earlier this year by then UK prime minister, David Cameron. Photograph: Christophe Ena/AP

Polls have shown that Le Pen will make it to the final round of the French presidential election next spring, but fall short of actually winning. But the parliamentary elections that follow are just as important, and could see Le Pen’s party make big gains. Brexit – which reinforces Le Pen’s stance against immigration and her calls for a similar in-out EU referendum in France – comes in handy for the party’s election machine.

Mantes-la-Ville echoes the concerns of many in English towns who voted to leave. With a population of 20,000, it was once a town of factory workers with several large plants, including one making clingfilm. De-industrialisation hit and many of those factory jobs have been lost. Unemployment is higher than the local average.



“Well done Britain, getting your autonomy and independence back,” said Natalie Aubry, 48, who ran a beauty parlour and tattoo business. “I think the European Union is nonsense really.”



Aubry, who plans to vote for Le Pen as president, said of the traditional French political class: “Those in power are liars and manipulators, arrogant and only interested in their own profit, not in people like us.” She praised the Front National mayor for “rubbish collection and keeping streets clean” as well as making people feel “safer”. Although she didn’t agree “100%” with Le Pen’s programme, she said she would vote for her as president because she wanted French sovereignty back. “Marine Le Pen is more loyal to France than anyone else who has been in government. Le Pen is a woman who loves France.”



One 52-year-old head of a local security company, who did not want his name published, had voted for the rightwing former president Nicolas Sarkozy in the past but would not do so again. “I used to be pro-European Union, but now I think it brings us more problems than benefits. At some point, we have to just stop immigration once and for all, stop letting people in. Politicians here always say they will act on immigration, yet they never do.”



Florence Faucher, professor of political science at Paris’s Sciences Po University, said there were parallels between Front National voters in France and those who backed Ukip in the UK, particularly the sense of those who felt “left behind”, who hadn’t benefited from globalisation, feared the insecurity in the job market and worried about their future. But she said the Front National, “even if it is strong on sovereignty, remains much more anchored in its old anti-immigration stance”.

Whether Brexit affects the Front National’s showing in 2017 depends on how smoothly Brexit goes for the UK. If things get messy, it could weaken Le Pen’s argument for a French exit, or “Frexit”.

“The first reflex, once the Brexit result came out, was to say ‘yes, Brexit is an advantage for the Front National and all the similar parties in Europe’. But the truth is it’s a bit early to say,” said Jean-Yves Camus, political scientist and expert on the Front National.



Camus said Le Pen could benefit from the fallout from Brexit in two ways. If it worked, the Front National could say Britain was leading the way in leaving the EU. And if the Brexit vote was somehow not respected by Westminster, Le Pen could be bolstered in her outrage. “The Front National could say that the British public voted by a majority to leave and their vote wasn’t taken into account,” Camus said.



Le Pen has promised an in-out referendum on French membership of the EU if she wins the presidential election. But for the time being, any Frexit is unlikely. Although French voters are increasingly critical of the EU, they are much less clear cut about it than the British.

“It’s more nuanced,” said Didac Gutierrez-Peris of the pollsters Viavoice. “In France, people can be critical of the EU while at the same time not wanting to actually leave the EU.”

A Viavoice poll of French people after the Brexit result found 68% felt decisions made in the EU had gone “in the wrong direction” in recent years. But 61% thought if France left the EU, there would be negative consequences.



Flowers placed next to a picture of French policeman Jean-Baptiste Salvaing and his partner, Jessica Schneider, who were killed last month in Magnanville. Photograph: Dominique Faget/AFP/Getty Images

“I don’t think France would ever leave Europe,” said Michel Boucher, a retired confectionery salesman from a quiet residential street in nearby Magnanville, where last month a man claiming allegiance to Islamic State carried out a gruesome murder of a police commander and his partner.

“We don’t vote Front National, but we do understand why people turn to them – because they’re so fed up and angry about unemployment, the economy or what they see as too many foreigners in France,” said his wife Syvlie, a retired childminder.

“People vote Front National because they want to change things and to strike fear into the political class, and in any case I can only see that increasing.”

