Ken Loach has accused Your Party of squandering an opportunity to unite the left in the fight against the far right after the upstart socialist movement founded by the former Labour figures Jeremy Corbyn and Zarah Sultana became mired in infighting.

“There was great hope when Jeremy Corbyn and Zarah Sultana joined forces; 800,000 people expressed interest – that’s three times the size of a political party,” he said. “But I’m afraid some of the behaviours were very poor and they lost a historic opportunity.”

The British film director and longtime Corbyn ally spoke to the Guardian before an official Cannes film festival screening of Land and Freedom – 31 years after the Spanish civil war drama first premiered on the Croisette.

The film follows a British communist who travels to Spain expecting a united anti-fascist struggle, only to encounter bitter ideological divisions between competing leftwing factions – tensions Loach believes remain deeply relevant today.

He said: “The split on the left was very important to explore in the film. It contributed to the defeat in Spain.”

Loach, who was expelled from the Labour party in 2021 after refusing to disavow other removed members, said mainstream political parties had increasingly adopted rhetoric once associated with the far right. “The Conservative leadership uses the same language as Nigel Farage, and the Labour right responds to that,” he said.

“The people who have nothing are always blamed, and the people who got rich on the system escape. They’re the ones now funding the far right. They fund Trump. Farage’s £5m is just the tip of the iceberg.”

Loach remains virulently critical of Keir Starmer’s leadership, describing current tensions within the government as “a case of when thieves fall out”.

“It’s no surprise people have turned against Starmer’s government. He cannot communicate, which is a fatal flaw in a politician. Tony Blair did dreadful things, but he had the gift of being able to communicate with people,” he said.

“There is no relation to the labour movement or the interests of working-class people. They’ll do all they can to keep Andy Burnham out of the running because he’s just slightly to the left.”

Land and Freedom, which received Cannes’ Fipresci international critics prize and the Ecumenical jury prize in 1995, has been restored in 4K and will screen in the festival’s Cinéma de la Plage strand on Tuesday.

Loach, who turns 90 next month, is the most selected and decorated director in Cannes history. He has had 15 films in competition and won two Palme d’Ors, for The Wind That Shakes the Barley and I, Daniel Blake. His longtime collaborator, the screenwriter Paul Laverty, is a member of this year’s competition jury.

“It’s extraordinary to be back with this film,” Loach said. “It’s about the first war against fascism. When we made it, our feeling was that fascism wouldn’t arise again. And now, of course, we face the far right again, but they don’t come in jackboots this time, they come under a different guise.”

Loach said the themes of the film – racism, division and economic insecurity – had become newly urgent across Europe.

“The language they use against immigrants, the racist undertones, finding scapegoats while refusing to look at the serious issues that are causing poverty and wars … they provide someone to blame for the sense of panic and insecurity people feel, they stoke up the hysteria.”

The director criticised fellow film-makers who argue cinema should remain separate from politics, referencing comments made by Wim Wenders during this year’s Berlinale.

“I was very disappointed to see my friend Wim Wenders say film-makers had to stay out of politics,” Loach said. “The difficulties people face are determined by the political choices we have available, and the power we have over the political process. So politics is absolutely central to film-making. Film-makers should be witnesses to our times.”

Loach argued that anger over Israel’s war in Gaza had galvanised political activism internationally, while creating an atmosphere in which artists who spoke out risked professional consequences.

“When people do speak out on this, they are being very brave, because it can threaten your career.”