OFTEN we never know the consequences of our actions. Sometimes, it takes the passing of a few decades. Bob Fulton, Robert Somerville, John Keenan and Stuart Barrie, workers at the Rolls Royce factory in East Kilbride, couldn’t have foretold the impact of their refusal in 1974 to work on the engines sent by Chile for essential maintenance.

Like many around the world, they had seen the images of the air raid on the Modena, the seat of President Salvador Allende’s democratically elected leftist government. The bombardment, on September 11 1973, had been ordered by the army, led by Augusto Pinochet. The rockets fired by the Chilean Air Force were from Hawker Hunters, one of Britain’s most exported military aircrafts. At the time, only one place in the world could service them: the factory in East Kilbride.

For four years the engines rusted in crates outside the factory until one night in 1978 they vanished. The workers were told their actions had changed nothing.

When Pinochet’s regime finally ended in 1990, more than 3000 Chileans were dead or “disappeared”.

Many thousands more were sent into exile, including the journalist father of Felipe Bustos Sierra, the director of Nae Pasaran, a feature-length documentary which has its world premiere tomorrow night as the closing film of the Glasgow Film Festival.

“The story of the coup was the dominant story of my childhood,” Bustos Sierra says. “Nae Pasaran is hopeful, but that is not the story of the dictatorship – that was about brutality, disappearance and death. As a teenager, I found it all a bit much, all this blackness, and I shunned it all for a bit.”

Bustos Sierra returned to the coup via his interest in the cultural movement that attended Allende’s rise. While researching the story of Victor Jara, a musician-artist tortured and killed by Pinochet’s soldiers, he met activists involved with Chile solidarity movements in the UK during the dictatorship.

“That was my first connection with the story of East Kilbride,” says the director. “People would point at photographs and say, for example: ‘That was the guy who would call us from the phone box by the factory and tell us what was going on. We don’t know what happened to him.’ And that was Robert Somerville.”

The National:

It took Somerville six months to get back to him, Bustos Sierra says.

“He was like: ‘I hear you are looking for me?’ Through him I met Bob Fulton, John Keenan and Stuart Barrie. To be able to put names to real faces and hear about their personal motivations was all very relatable to me.

“They were quite wary at first though,” he continues. “What would be the point if it was just going to be a rehash of the past? Because their story had never had an ending to it, I suppose they didn’t perhaps want to relive it if that’s how it was going to stay. John Keenan said: ‘Do you think you could find the engines?’ That became the main propeller forward. But this film was always not just going to be about the past.”

The past itself, in Chile as in every country with a turbulent history, is often contested.

“Over the years I have met many people with a connection to Chile and it was always to do with resistance to the dictatorship. A problem that would always emerge was of finding out what really happened versus how much we had invented to keep morale up,” Bustos Sierra says.

“The story of the Scottish workers was a very colourful one as it was tied up with the most iconic image of the coup – the Hawker Hunters attacking the capital. But information was scarce and there were Chinese whispers so that the story became about the planes themselves being stuck in the factory and the workers had erected barricades and were fighting with the police everyday. It was very exaggerated. If this was going to be a relevant story to tell today, a big part of it for me was to separate the fiction from what really happened.”

Official archives posed challenges in both countries: in the UK much was redacted. In Chile, apart from some files which survived the Modena bombing, much simply did not exist. As the Pinochet regime was ending following a referendum in 1988, government information was destroyed, wiping out a whole period of Chilean history.

So when one of Nae Pasaran’s interviewees, Humberto Arenas, an Allende-sympathising mechanic in the Chilean Air Force until the coup, says a woman claiming to be from Amnesty UK told him he was on a list of political prisoners being released in exchange for engine parts, nothing as yet can verify or disprove his claim.

As a note at the end of the film says, both Rolls Royce and the UK Government did not respond to Bustos Sierra’s interview requests.

“That’s the only thing in the film I present without any other evidence,” he says. “That was why it was important to get the people from Amnesty in the film. I’ve heard people say that back then this was a rumour, and I think the people who may have been involved have passed away. The archives on the release of the Chilean political prisoners are not to be released – I think – until 2039. But I’ve interviewed Humberto twice and he believes it. And maybe that gave people some hope back then, so I think it is valid to include it.”

Nae Pasaran often illuminates a whole aspect of the era, or a deeper question about human nature and ethics, with elegant brevity. A particularly striking moment is when Raul Vergara, a captain in the Chilean Air Force until his support for Allende landed him on the wrong side of the coup, expresses his lack of bitterness towards his captors, even though “some of my torturers appear in my wedding album”.

A major flashpoint of the Cold War, the coup was stoked by economic sanctions and artificial shortages ordered by US President Nixon, whose government supported the junta in consolidating power.

As the late Dr Arturo Jiron Vargas, Allende’s health secretary and personal physician, notes: “After the coup, the shortages stopped.”

“Nationalising the copper was no small matter but we did it anyway,” he says. “And we paid the price.”

Striking, too, is Bustos Sierra’s interview with General Fernando Rojas Vender, former Commander in Chief of the Chilean Air Force and Hawker Hunter squadron leader. In his first interview to camera, Vender is asked why he thought Bob Fulton, a Christian and veteran of the Second World War would lead a band of men in Scotland who refused to work on Chilean engines.

Politics,” says Vender.

“He could not understand their motivation,” says Bustos Sierra. “He’s a very Christian man, and the Chilean Air Force was modelled on the RAF. So to someone like him British society was the epitome of civilisation. And yet I couldn’t get him to be philosophical about it, or be a little introspective and find some empathy, put himself in someone else’s shoes.

“That was something that everyone else in the film could do, even briefly. I thought it interesting that someone with such a rich life could have such a low opinion of others.”

For Fulton, who had heard of the torture and persecution through his church, and Somerville, Kennan and Barrie, it was an immediate sense of solidarity with the people of Chile that made it impossible to repair those engines.

It’s frequently noted in the film – which is hoped to be out on general release in September to coincide with the 40th anniversary of the coup – that “they could be me”. As too is the belief that such a boycott could have only been successful in a time of trade union strength.

“The guys know that if they did this today they would be arrested,” Bustos Sierra says. “The boycott ended in 1978, the year before the election. You can see in Hansard that the Tory opposition were utterly baffled that it had got this far. Trade unions were getting in the way of British business, and whatever the Chileans were up to was their business.

“I can see the direct line: that the Conservatives wanted to make sure that nobody could ever do what the guys in Scotland had done. A few years later there was the miner’s strike and the subsequent reduction in the power of trade unions. I’m not saying that was a stepping stone, but that somebody was taking notice.”

Tomorrow, 7.30pm, Glasgow Film Theatre, sold out. glasgowfilm.org www.debasers.co.uk