The tramline that snakes through Parla passes an Extremaduran food shop dense with chorizo, cheese, ham and honey, a billboard for a real estate company catering to the Chinese community and the Titanic grocery shop, which offers couscous and not just halal meat but “100% halal meat”.

On either side of its winding tracks, on shopfronts, on faces, on clothes and in the conversations overheard on the streets, is written the story of the many and varied communities that have fuelled Parla’s growth over the past 50 years, transforming this small town half an hour from Madrid into a commuter sprawl of 128,000 people. Despite the town’s proximity to the capital, many of its residents feel overlooked and forgotten by successive central, regional and local governments.

The economic boom that swelled Parla’s population in the fat years that preceded the 2008 crash was rooted in people more than planning, and today, long after the bubble burst, the town is struggling with an unemployment rate of 14% and a lack of schools, medical centres and amenities.

That lack has not gone unnoticed by the upstart Vox party, which is expected to pick up around 10% of the vote in the general election, making it the first far-right grouping to win more than a single seat in parliament since Spain returned to democracy after General Franco’s death in 1975.

People from 115 different countries account for 22% of Parla’s residents – a fact not lost on Vox supporters in the town. “For me, it’s about the economic crisis, immigration, education and healthcare,” said Tomás Ramos, a 42-year-old self-employed Parla resident. “I think that the children of immigrants have to enter the school system, but there are 16 schools here and they will change the ratio of teachers and pupils. Then you have the question of culture and language. Having 13 different languages in the classroom is going to change things more than having two or three.”

They’re giving immigrants loads of money and that’s breaking the pensions system Francisco Sánchez, Vox supporter

But, said Ramos, voting Vox was about more than that: “It’s about renewal and changing things for those of us who have heard other politicians making promises but not delivering once they’re elected.”

Trust in politicians is in short supply here and elsewhere in Spain, and Vox’s bid to lure conservative voters from their traditional home in the People’s party (PP) looks to be paying off. Some traditional PP voters remain angry over the slew of corruption scandals that brought down Mariano Rajoy’s PP government last year, while others think that the party missed a trick by not taking the tougher line on the Catalan independence crisis advocated by Vox.

Parla’s town council, traditionally a stronghold of the Spanish Socialist Workers’ party (PSOE), has been in the hands of the PP since the 2015 municipal elections. Its socialist mayor resigned seven months earlier after being arrested in connection with a massive corruption scandal. But things are complicated for the local PP, too. Earlier this week, the PP’s former general secretary in Parla defected to Vox, highlighting the fractures that the Spanish right is suffering both locally and nationally.The new candidate declined to speak to the Observer, and a party spokesman was reluctant to comment on its strategy in towns such as Parla.

Francisco Sánchez, 59, an unemployed former security worker, was more forthcoming. He sees Vox as an alternative to the PP and PSOE, which, between them, have governed Spain for four decades. “Vox have concrete policies on national unity,” he said. These, according to its manifesto, include suspending Catalonia’s self-government “until the defeat of the coup plotters” behind the bid for regional independence and the “outlawing of parties, associations and NGOs that strive for the destruction of the sovereignty and territorial unity of the nation”.

Immigration is also a worry for Sánchez. “They’re giving immigrants loads of money and that’s breaking the pensions system,” he said. “And these are people who don’t work and just ask for money.” He dismissed any suggestion that Vox is a racist party. “That’s the narrative of the opposition – of all the parties who agree with each other,” he said. “Anyone who is proud of being Spanish is called a fascist. But fascists impose their will on others. Vox doesn’t impose its will on others and it’s not violent. And yet they call us fascists and spit on us.”

Spain’s prime minister Pedro Sánchez at at campaign rally. Photograph: Sergio Pérez/Reuters

Spain’s socialist prime minister, Pedro Sánchez, has warned the electorate against complacency in the face of Vox. The PSOE is expected to fall short of a majority, and there has been speculation that Vox might join forces with the PP and the centre-right Citizens party to form a coalition if it wins enough votes. A similar agreement ended decades of PSOE rule in Andalucía last December following the regional election that saw Vox break through and pick up its first 12 seats.

“No one thought that Trump would be president in the US, nor Bolsonaro in Brazil,” Sánchez tweeted on Friday. “And people reckoned Brexit wouldn’t happen either. A vote for the PSOE is the difference between a Spain that looks towards the future and a Spain that slides back 40 years. No one should stay home on Sunday!”

Leticia Sánchez, leader of the Parla branch of anti-austerity Podemos party, is also worried by the emergence of Vox in the town and others like it. But, she points out, its support has not materialised from nowhere. “We’re not seeing a new load of people coming here and doing this,” she said. “The PP here has split in two and the most conservative part has gone over to Vox. We hope that means there will be a split in the rightwing vote here between the PP and Vox because these aren’t new votes.”

Leticia Sánchez notes that it is not only political parties opposed to Vox that are taking a stand. At the beginning of April, hundreds of people from neighbourhood groups and citizens’ platforms staged a demonstration in the nearby town of Leganés to condemn the far right. Sánchez and Parla’s mayor, Luis Martínez, fear Vox could win representation on the town council in next month’s municipal elections. Martínez warns that whoever governs Parla must govern for all its inhabitants. “This racism problem, with its focus on people from abroad and people of different colours, is about white supremacism – and that’s something that has to be utterly rejected,” he said. “It’s also hiding the real problem, which is the shameless people who don’t want to work: and they could very well be Spaniards with a dozen Spanish surnames who are claiming benefits and perpetrating fraud.”

The mayor says Spain’s low birth-rate means it needs immigrants, and has a simple message for anyone trying to stoke fears and stir up tensions: “Parla isn’t the place for you.”