When Sam Mendes was small, he would laugh at his grandfather’s habit of forever washing his hands. His father took him to one side. “It’s because he remembers the mud in the trenches,” he said, “and never being able to get clean.”

Sam stopped laughing. He asked his grandfather, then in his mid-70s, to tell him more about the war. After five decades’ silence on the subject, “he finally cracked. And he told us loads and loads of stories, especially after a couple of rums. He was very theatrical and charismatic and Edwardian. He was also quite deaf, so he shouted them all.”

Alfred Mendes was 16 when he enlisted, excited at the chance to serve in a good war that was going so well. When he got to the western front, “he just couldn’t believe what he found. His stories weren’t about bravery, but how utterly random it all was.” His small stature meant he was often chosen as a messenger. “That image of that little man, cut adrift in that vast, misty landscape, really stayed with me.”

After the war, Alfred moved to Barbados, became a civil servant, wrote socialist novels and died in 1991, aged 94. At 34, Sam won the best director Oscar for his debut, American Beauty; 20 years later, a movie inspired by Alfred’s stories may bag him another.

1917 review – Sam Mendes turns western front horror into a single-shot masterpiece Read more

The film, 1917, is Mendes’s first since Skyfall and Spectre and clearly intended as an antidote to 007. Both Bond movies were “chaos”, he says, making noises that indicate months-long logistical migraines, high-wire acts of placation and compromise.

This film has one linear storyline and just one long shot – well, really a couple of dozen, invisibly stitched together by the cinematographer Roger Deakins. Two young lance corporals, Schofield (George MacKay) and Blake (Dean-Charles Chapman) are hauled in front of their general (Colin Firth) and given a mission. They must shin up the dugout, race across no man’s land (mind the barbed wire, gunfire, rats, craters and corpses), along the (abandoned, probably) enemy trenches, through a French countryside strewn with booby traps, then find an adjoining battalion and tell them to call off their dawn attack as they would be advancing into a trap. If the pair fail, 1,600 men – including Blake’s brother – will die.

Originally, says Firth, his scene was yet more brutal: as the boys hurry off to almost certain death, an orderly unfurls a white linen tablecloth for the officer’s high tea. That was scrapped. “The military establishment’s indifference to the wellbeing of these two young men was abundantly clear without that kind of emphasis,” says Firth, “or making it about the callousness of one particular general.

“The mission the boys are sent on is one of brutal necessity, a tragedy compounded, of course, by the fact that the war itself was not.” Firth is only on screen for a few minutes, but filming even that short scene made him reassess his feelings. “One could empathise with the powerlessness and terror of young men who had no say in their fate, acting on decisions made by old men.”

Facebook Twitter Pinterest It’s like this, men … Colin Firth as General Erinmore. Photograph: François Duhamel/AP

The tablecloth edit is a clever one. In its light-touch handling of the conflict’s class battle, 1917 distinguishes itself in its genre. “Once you start on all that,” says the films’ screenwriter, Krysty Wilson-Cairns, “you’ve lost most of your audience. And in Scotland, anyway, it means nothing.”

Wilson-Cairns is a 32-year-old Glaswegian, perky in a jumpsuit. This is her first film. Her formative cinema experience came as a teenager in 2003: “I saw Charlie’s Angels: Full Throttle and I was blown away. After that I knew I either wanted to be an Angel or to work in the movies. And Charlie wasn’t taking applications.”

Her gender has raised eyebrows given 1917’s subject matter, she says, grinning, “but I somehow negotiated my vagina through it”. And she does suspect it means the stakes in the screenplay skewed differently: the aim is to get home, rather than to slaughter as many of the enemy as possible. “You’re not holding your breath to see if he will make the shot, but knowing that if he doesn’t, he’ll never see his family again.”

One of Wilson-Cairns’s own grandfathers didn’t serve in the armed forces, but he was evangelical about educating Krysty about war. “He told me that understanding history is the only way to avert future catastrophe. The first world war was the stupidest thing humanity ever did to each other.

“But although it was misguided, those men were also fighting for a free and united Europe. And somehow that’s under threat again, out of sheer madness and folly and political gain. Peace is so tenuous. I pray to God that we don’t have the same outcome.”

Facebook Twitter Pinterest Krysty Wilson-Cairns was given an early grounding in the futility of war by one of her grandfathers. Photograph: Jean Baptiste Lacroix/WireImage

Both she and Mendes separately say they want the film to act as a corrective to a repackaging of the war in the service of jingoistic isolationism. “People who are attached to some sort of nostalgic vision treat these wars retrospectively as triumphs,” says Mendes. “In fact, they were tragedies.

“That kind of hijacking of shared cultural memories and pride is very subtle, and very easy to do. At the moment, it happens all the time. ‘We’re going back to being on our own again! This is the spirit that fought two world wars!’ That’s what we’re now lumbered with.”

And while the volume rises on such dodgy tub-thumping, so the values that meant people were prepared to lay down their lives have been eroded, Mendes thinks; it’s only extreme environmental activists who are today doing something analogous.

“Sacrifice has fallen out of fashion,” says Wilson-Cairns. “The idea of having something above you, something to die for, is becoming an antiquated notion. People are inherently more selfish and more self-obsessed nowadays.”

Mark Strong is among those actors – Firth, Andrew Scott, Benedict Cumberbatch – who pop up for cameos as the boys’ superiors; bit parts whose starriness some have found distracting. Strong agrees there has been a slump in altruism. But that is chiefly the lookout of the institutions, he says, not the people beholden to them. “I’m not sure it’s an issue of no longer understanding sacrifice, but more that collective responsibility is giving way to protection of self-interest. Not just in Britain but all over the world, there seems to be a move to secede from the collectives that were created – for better or worse – after the two wars, whether Catalonia or Scotland or the breakup of Yugoslavia and the Soviet Union.” He gives Trump a name check, too; not the most inspirational model of magnanimity.

Both 1917’s leads say they hope they would do the same as their characters in the circumstances. Still: fingers crossed it’s not tested. If conscription came back today, says Chapman, “it’d be all over Twitter”.

Facebook Twitter Pinterest Watch the trailer for 1917

At 22, the former Billy Elliot and sometime Game of Thrones actor is the youngest and chirpiest of the cast – and the one least versed in the war before the shoot began. Making the film, he said, “I had so many reality checks: ‘Cor, have I got it easy!’” He read a collection of contemporaneous diaries between takes, and was especially taken by one written by a man who was in the cavalry, shot in the hip and spent four days paralysed in no man’s land. “It turned out it was my great-great grandfather! He went on to work in the first poppy factory in Richmond.” Chapman is proud and awed, but hasn’t investigated any further.

MacKay, 27, gentle and diplomatic, is wary of damning his – or any – generation. Our unfamiliarity with the need to give up everything is only for the good, he says. And how do you understand hardship if you’ve known nothing but comfort; he talks about wanting to grow his own veg.

“We’re less in touch with what really matters because we’re not being stretched. The film is about being at your absolute pits. You don’t want to be in a place where you only have what you need. But we’re perhaps rather too far down the other end of the scale and need to stop before we exhaust everything.”

MacKay is 1917’s true breakthrough. Familiar from the likes of Pride and Sunshine on Leith, this film – plus Justin Kurzel’s upcoming Ned Kelly movie – should make him an A-lister. Mendes cast MacKay partly, he says, because his face and demeanour suggested old-fashioned qualities of dignity and virtue. MacKay couldn’t possibly comment, but says he based Schofield on his own grandfather, for whom he was named, and who was a man of honour and tact.

In the film, neither Blake nor Schofield speak about their feelings; they don’t need to – nor do they have time. Mendes was surprised, he says, at how many American viewers identified 1917 as a singularly English film because of this. “It’s about telling the truth in the face of great difficulty. The classic example is Brief Encounter; a particular way of handling great emotion.”

MacKay cautions against rose-tinting reticence. “Stiff upper lips can be very unhealthy. Denial is rarely good. But there’s a real depth of resolve to swallowing something for the now. There’s weight, like an ocean. Under the surface, there’s so much bottled that, when it does break, it’s bigger than those that break all the time.”

Watching the film, says MacKay, “made it very clear to me who I want to come back to in my life, who means the most to me.” Usually, seeing yourself on screen isn’t easy, he says; this is the first time he has been transported – thanks to the shooting style. “You take every step with those men. Making it meant a lot to me. But watching it did, too,” he says.

And it is this coup de cinema which most marks out 1917 and makes it feel as uncomfortable, and as peculiarly modern, as László Nemes’s Holocaust drama Son of Saul. The audience is unable to look away or avoid the brutality. And while most first world war films are slow-burns of claustrophobia and paralysis, this is queasily kinetic: a horrifying rollercoaster taking you on a nightmarish heist.

Facebook Twitter Pinterest Sam Mendes on set with Dean-Charles Chapman (left) and George MacKay. Photograph: François Duhamel/AP

Yet not everyone has been convinced. Some reviewers have found the single-shot style too gimmicky; an exercise for the sake of it, a display of technical prowess that distracts from the action. Mendes scoffs. “The camera never goes through a keyhole or passes through glass or follows the course of a moving bullet.” For him, it’s a cineaste’s complaint, not a concern for the punters.

Deakins is downcast about the detractors. “It’s a pity,” he says. “Some people have told me they’re very aware of the camera.” He looks more hopeful when I wonder if it’s an old fogey issue. “I think the film will appeal to a younger generation raised on video games because of that more immersive feeling,” he says. “It’s not a piece of classical film-making.”

Still, when a friend of Chapman’s told him it reminded him of a first-person shooter game, he baulked. “You control that. With this film, there’s no control. That’s why it’s so terrifying to watch: you can’t escape.”

Wilson-Cairns is, characteristically, more frank. “The whole point of this movie was to live 115 minutes in someone else’s life. If you noticed the camera, we would all have failed. We didn’t make it so you would look at your phone. Or have it on in the background. Or so that someone somewhere would make a fuckload of money.”

What she wanted above all, she says, was veracity. There are historical dramas whose primary duty is entertainment. She was unbothered by liberties taken in, say, last year’s Mary Queen of Scots: colour-blind casting, fact-massaging, anachronistic dialogue. Those weren’t appropriate here, she says. “We had to pay homage to the reality these men suffered through. We didn’t want to inflate it or deflate it. People lived this. It’s not a spaceship. It’s not a fantasy.”

Deakins has a slightly different take. “It’s not naturalistic,” he says. “If you really showed what it was like, you wouldn’t have anybody in the cinema after five minutes.” Still, he was buoyed by Mendes’s backbone when they were shooting a hospital tent scene near the end. “He said: ‘We can’t pussyfoot around. We have to do it justice.’ I remember saying: ‘I think we’ve earned it. We should have, by this point.’”

And what of Alfred Mendes? What would he have made of the film, of the upshot of finally sharing his stories? His grandson pauses. “I think he would have found it extremely uncomfortable to watch. But I’m sure he would have appreciated its existence.”

• 1917 is released in the UK on 10 January