I first ask Paul Greengrass about the stunning pyrotechnic effects in The Lost Bus. The galloping disaster film stars Matthew McConaughey and America Ferrera as a bus driver and a teacher seeking to rescue a class of children from the deadliest brush fire in California history. It looks like a dangerous operation.

“Let me talk a little about how we made the film,” he says. “Then let me talk a bit about visual effects. It’s quite interesting if you want me to give it some length.”

No! Greengrass, a former TV newsman who reinvented the action flick with The Bourne Supremacy, is among the most genial of film-makers. He is also, in my experience, the talkiest man on the planet. If he answers at length, that will be the only question we get into our allotted time.

Anyway, he gives me a speedy 800 words on how he settled on using largely practical effects.

“The truth is, when I started, when I set out to make this, I thought I was going to do the bus section virtually,” he begins. “Because I went to see the U2 show at the Sphere in Las Vegas. And I was so absolutely knocked out by that big screen. When they played Where the Streets Have No Name and they went to the desert, you absolutely believed you were in the desert. It did make me think technology is now at the point where you literally can’t tell.”

Greengrass spent some time “going down that road”. But he ultimately felt his heart wasn’t in it. “I just wanted to be in a real world,” he says. “So we went in the other direction.”

The result, reimagining true stories from the 2018 Camp Fire in northern California, delivers all the crashing, clattering action you expect from Greengrass. But there is also a sombre warning about climate change.

“I want young people to see this film,” he says. “Anyone who’s got a care to whether the world is burning.”

Throughout his career in feature films, over riveting work such as Bloody Sunday, Captain Phillips and United 93, Greengrass has had smart alecs such as me asking about the influence of his time on TV current affairs. Raised in Surrey, in southern England, to an ordinary family, he made his way to Queens’ College, Cambridge, and on to work as a director on the pioneering ITV show World in Action.

It is impossible to shake that comparison when considering his famously kinetic camera movements in movies. Is his work still informed by that early training?

“Profoundly! Honestly, profoundly!” he says. “I was very young. I was 21 or 22. I was really a baby. I’d only been in television a year and suddenly I was pitched into this world, with these hairy-ass documentarymakers. Ha ha! It was a rough apprenticeship in those days. They came in, saw your puny efforts at film-making, and they would tear it to shreds.”

In the early 1980s he got to see all corners of the planet.

“I was expected to go to war zones. To cover apartheid in South Africa. I was in Central America. Or the miners’ strike in the north of England for World in Action. And I had to bring back a film. That taught me what the world looks like.”

As he passed 30, Greengrass moved into TV drama. He admits to feeling an inner confliction. Having spent his early years representing reality, he was now manufacturing it. There is always a conjuring trick at the heart of fictional film-making.

“It took me until my 30s, while I was working through those television dramas, to find my voice and find a way to do it,” he says. “I found an aesthetic to shape the types of stories that were true to where I’d been, that existed in the world I had been operating in.”

That makes sense. The One That Got Away, from 1996, telling a story from the Gulf War, gave a hint of Greengrass’s later gift for action cinema. The Murder of Stephen Lawrence, starring Hugh Quarshie and Marianne Jean-Baptiste, from 1999, examined the slaughter of that young black Londoner with energy and sensitivity.

It feels as if it all came together with Bloody Sunday, in 2002. Shot in Derry and north Dublin, the film combined economic character studies with a chillingly effective re-creation of the notorious 1972 massacre in the Bogside.

Two years later Greengrass returned to Ireland to shoot Omagh for the rising producer Ed Guiney – later Oscar-nominated for Room, The Favourite and Poor Things. It feels as if Greengrass was there to watch the current boom in Irish cinema kick off.

“Jim Sheridan was executive producer on Bloody Sunday,” he says. “So he was one of the builders of your industry. Then, on Omagh, I worked with Ed Guiney, who would be one of your leading figures today.

“So, between those two hugely talented and gifted people, you could feel where the industry had come from and where it was going. You could feel there was so much talent there.

“I must come back. Ed and I have been talking, over the last 12 months, about making something together back in Ireland.”

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A huge Texan enters the room and embraces Greengrass. It is McConaughey. They josh and tease. McConaughey says he is off to “get a hot dog”. We return to the conversation.

The move from gruelling dramas of the Troubles to the second film in the Bourne espionage sequence was not an obvious one. But it involves no hyperbole to suggest that The Bourne Supremacy, from 2004, proved among the most influential films of the new century.

Greengrass’s rapidly moving camera and crunching sound design brought a balletic fluidity to action cinema that everyone else then tried to copy. Few articles on the James Bond reboot, with Casino Royale in 2006, failed to credit Greengrass’s work on Bourne.

“I found my voice,” he says. “I knew what my films were meant to feel like. So when I had the chance to go and make a big commercial movie, that felt like a new adventure. But I wanted to make a film that felt authentic.

“I didn’t know whether that would work out, to be absolutely honest, because there’s so much baloney talked about working in Hollywood. But the truth is, it’s actually incredibly permissive. It was quite transgressive, but they never said ‘Don’t!’”

Looking back with 20 years’ hindsight, “transgressive” sounds like an odd work to use. But this was a clash between two distinct film-making traditions.

“I saw it as my old-fashioned, British, social-realist documentary aesthetic,” he says. “That was very much hand-held, very much about zoom lenses – getting back and observing. It was quite an unshowy, unsentimental aesthetic. It suited the Bourne landscape, but it still felt quite radical.”

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Not so much now. Greengrass remembers shooting The Bourne Ultimatum at Waterloo Station, in London, a few years later and being surrounded by accidental acolytes. All the kids had mobile phones and, like Greengrass, they were shooting on the move.

“What I thought was a very old-fashioned aesthetic was what the under-30s – and particularly the under-20s – were then doing,” he says. “They were seeing images on their mobile phones, which were all hand-held and very unstructured.

“So anything that was structured felt old-fashioned to them. What I was doing, when reaching back to the 1960s and 1970s, now felt contemporary.”

We speak as The Lost Bus premieres to much hoopla at Toronto International Film Festival. The film unspools on a huge screen before many celebrities. But, as an Apple TV+ title, it will, despite a brief cinema release, play to the public largely on the small screen. That seems a shame for such a dynamic action film.

“I’m not someone who decries progress,” Greengrass says. “If you’re going to continue to work and continue to have the privilege of making films, you’ve got to go with how it goes.”

He expresses his gratitude to Apple. He enjoyed working with Netflix on the underappreciated period drama News of the World. But there was once something else.

“I can remember, as a kid, watching The Sound of Music and being absolutely entranced,” he says. “I remember my late sister took me, and I cried and cried and cried.”

He didn’t see it again until it popped up on TV six or seven years later.

“The audience for this film will see it 100 times more in all the various different ways that it can be accessed,” he says. “That’s progress, and that’s okay.”

The Lost Bus is in cinemas from Monday, September 29th, and on Apple TV+ from Friday, October 3rd