In the first round of the French presidential election on Sunday 23 April, Gwendoline, an 18-year-old from Hénin-Beaumont, a small northern town of 26,000 inhabitants, voted for the first time, for Marine Le Pen. Le Pen cast her own ballot in Hénin-Beaumont too. The Front National mayor, Steeve Briois, was elected in one round of voting in 2014.

I met Gwendoline in a windswept railway station parking lot, on 1 May, as we were waiting for a bus to take us to Hénin-Beaumont. Our train had been cancelled. She laughed at how grim her bank holiday Monday had turned out to be – stuck in a car park on her way back from a funeral, with a mock baccalauréat exam to look forward to the next day.

When the bus finally arrived, it took us very slowly across former mining lands, around a slag heap, not far from Oignies, where the last French coalmine closed in 1990. Gwendoline said that everyone in her class who was old enough to vote, voted for Le Pen. There wasn’t much to do in town, she said, maybe go to Auchan, the biggest shopping centre north of Paris, in the next town. ‘It's Hénin-Beaumont, it's not marvellous,’ she smiled.

Christopher Szczurek is an FN councillor in Hénin-Beaumont. ‘Marine was the only candidate to go for an election party outside of Paris,’ he told me. Emmanuel Macron held his victory party in La Rotonde, a brasserie in the sixth arrondissement. Le Pen, who spent most of her life in affluent suburbs to the west of Paris, celebrated in a sports hall in Hénin-Beaumont. According to the town council, there were more than 600 accredited journalists at the party. Le Pen first set foot in Hénin 10 years ago. In 2007 she ran for a parliamentary seat there and lost. The FN, currently under investigation on suspicion of campaign finance fraud and fake jobs in the European parliament, has steadily gained ground in the region since then.

Briois recently replaced Jean-François Jalkh as interim leader of the Front National, afer Jalkh was accused of Holocaust denial. The party claims to be less xenophobic and more socially concerned than it was under Jean-Marie Le Pen, and it’s attracting votes in a region with high levels of unemployment. Szczurek’s Polish name isn’t unusual here: people of all nationalities worked together in the mines and the factories which have closed down. He gave me a tour of the town hall, which is undergoing renovations. Its huge reception rooms and stained-glass windows of miners are a testament to the town's former glory. ‘I became a Front National member ten years ago,’ he told me. ‘Here, one could feel a new Front National appearing. People had the feeling they had been betrayed by traditional parties.’

The Socialist former mayor, Gérard Dalongeville, was arrested for embezzlement in 2009. After his fall, he wrote two books on corruption in the Parti Socialiste in Pas-de-Calais. Briois had been denouncing Dalongeville for years. ‘People would say they weren't necessarily pro-FN but thought his time had come,’ Szczurek said.

Tuesday morning is market day. Several older people I spoke to had positive things to say about the mayor, whom they call ‘Steeve’. (‘He's really nice,’ Gwendoline had told me. ‘I hope you get to meet him.’) ‘Si c'est Macron on sera marrons,’ a man sang. His friends laughed. (‘If Macron wins we'll be losers.’) The municipal billboards which are supposed to carry posters of both presidential candidates carried only one. ‘Marine’ is dressed in blue, hands folded, accompanied by the caption: ‘Choose France.’ Her last name, the name of her party, and the tricolour banner are gone. You could see where Macron’s posters had been torn down.

When Briois came to power, one of his first measures was an anti-begging decree, aimed at Roma people living in the city. It was later repealed by the administrative court. A year ago, the council adopted a charter called ‘My Town without Migrants’. It didn’t change much, as the prefecture had never asked the town to take in migrants. Over the years, the council cut funding to organisations that were giving help to migrants and homeless people. It said they were ‘political’. Claire Audhuy, a theatre director, ran a project for local children to meet migrant children. ‘When are the migrants coming?’ one little girl asked in the middle of a session. The ordinary children she was playing with weren’t the monsters she had been led to expect.

Marine Tondelier holds a council seat for Europe Ecologie Les Verts. ‘In history class I always wondered how fascism starts,’ she told me. ‘Well this is what we're experiencing.’ She recently published Nouvelles du Front, a book based on her blog, about everyday life in Hénin-Beaumont, in which she describes being humiliated and intimidated by the mayor and his team, in council meetings and on social media, including Briois's own Facebook page. Bruno Bilde, his communications director, is a member of Marine Le Pen's close circle.

The FN everywhere has a difficult relationship with the press. Since 2015, the council in Hénin-Beaumont has been at war with the local office of La Voix du Nord newspaper. ‘They expected us to do their PR,’ the local editor, Pascal Wallart, told me. ‘Once it became clear we wouldn't, they started calling us “enemies of Hénin-Beaumont”, “socialopes”.’ (Salopes means ‘sluts’.) The paper has lost all access to the council. It is routinely bombarded with rights of reply and ridiculed in the council magazine. ‘People look at this conflict as if they were watching a Tom and Jerry cartoon,’ Wallart said. ‘It makes them laugh.’ The FN works ‘like a steamroller’, he said, ‘repeating things until people think they're true’.

There was a small protest this week against the FN. More than a hundred people met in front of the swimming pool and walked the short distance to the town hall. ‘First, second, third generation,’ they chanted. ‘We are all migrants' children.’ Their neighbours looked on in silence. Nora, who is of Algerian origin, said she wasn’t angry with them. ‘It's a mix of naivety and suffering. But it's legitimised something nasty,’ she said. ‘My dad was a miner who came from Algeria in the 1950s,’ a woman called Sakina said. ‘I'm 54. I love my city. I'm not leaving even if they want us gone now. It's impossible to say the FN are not racist. Closing the borders. Giving priority to “the French”. How are these measures not racist?’

After school, Gwendoline took me to the shopping centre that caused so many shops in Hénin-Beaumont to close down. She said that some of her classmates who had voted for Le Pen were of North African origin. ‘They're not sure Le Pen is not racist but they have papers, they're not flagged by a fiche S and they respect the law, so they should be OK,’ she said. She had got into a fight at school. I realised she liked Le Pen because she saw her as an outsider. ‘I like Marine because she is frank. She refuses to be beaten despite the media being against her. Everyone deserves a chance,’ she said. After voting on Sunday morning, Gwendoline is planning to get a tattoo with the name of a friend who killed herself last year. ‘She just … didn't make it,’ she said, looking out at the green expanse surrounding the biggest shopping centre in Northern France.