“There’ll be no more of this shit,” snarls George MacKay, eyes bulging like a young Iggy Pop. “I’ll give you the full 11 inches of my dick, just so you can know how it feels to get shaaafted!” His temple throbs. His mouth froths. He gets so excited that he spills some of his lemon and ginger tea on the floor of the photo studio we’re sitting in. “Oh dear,” he says, Iggy Pop transforming rapidly into an extremely apologetic, polite young man. “I’m just going to wipe that up with my bum.” And so he does – sliding across the floor while his black trousers soak up the drink.

A polite young man George MacKay might be, but at just 27 he’s had plenty of practice trying on other personas: a closeted gay activist in Pride, a singing Scottish squaddie in Sunshine On Leith and – most recently – Lance Corporal Will Schofield in Sam Mendes’ first world war smash, 1917. He is soon to play the notorious Australian bushranger Ned Kelly in True History Of The Kelly Gang, which is where today’s unlikely punk outburst comes in: director Justin Kurzel wanted his young actors to put a punky spin on the tale of the Aussie folk hero, so he booked a gig venue and told them to perform their own songs live as a punk band. MacKay is treating me to one of his self-penned numbers.

“We put on dresses and rubbed ash in our eyes,” he recalls of the performance by the resulting band, Fleshlight. MacKay came up with the name: “It’s a… it’s a sort of… sex toy that you can, um, unscrew and, er, make love to,” he says, his bashfulness further proof that Iggy has left the building.

‘Just grow a mullet’: a beardless MacKay in True History Of The Kelly Gang

MacKay adores this immersive way of working – not just researching but living his roles. To prepare for True History Of The Kelly Gang, he lived in the bush, bulking up by chopping wood and riding horses. Sadly, not every aspect of physical transformation was as easy to achieve: the outlaw Kelly was renowned for his manly whiskers, yet baby-faced MacKay struggled to grow any facial hair. “I honestly thought I was going to lose the part,” he says.

What did his attempt at a beard look like?

“It looked like a big ginger eyebrow. I spoke to [Kurzel] on Skype, and of course at the time he had this amazing beard. just like Ned’s out here –” he gestures with his arms. “He said, ‘Well, no need for the whole one, but… like, nothing?’”

They tried a stick-on beard but Kurzel wasn’t convinced. Then the director had a brainwave – what could be more punk rock than playing Australia’s hairiest antihero with baby-smooth cheeks? “Just grow a mullet instead,” came the instructions, which MacKay managed.

Fortunately, no facial fuzz was needed for 1917, in which MacKay’s role – alongside another relatively little-known actor (Dean-Charles Chapman) – was to be a young man in an old man’s war. The story follows the two soldiers on their mission to carry a vital message deep behind enemy lines. Again, MacKay threw himself into the part: army boot camps, six months of rehearsals, understanding the function of every bit of archaic military kit. The Oscar-winning film was famously shot in “one take” (in reality, very long takes – some of them almost 10 minutes – stitched together) and the last thing anyone needed was to get seven minutes into a take, only for the safety catch on a rifle to jam.

Sometimes, though, mistakes were encouraged. In one epic scene, MacKay hurtles down the frontline while allied troops emerge over the trenches; he gets floored by one soldier, something that wasn’t scripted. “When everyone’s blood’s up and the bombs are going off, that happens,” MacKay says. “Sam wanted it to be natural and alive, so he kept it.”

As an actor, MacKay is already something of a war veteran: he’s fought the first world war three times, and the second world war twice. For him, this has meant delving into an awful lot of history books, including harrowing first-person accounts. “We talk about seeing the inside of a person in a spiritual or figurative sense,” he says. “But these people would really see it. To see someone’s organs, or their bone split and poke out. Picking up a friend’s leg and it coming away…” He shudders.

‘When everyone’s blood’s up and the bombs are going off, unscripted things happen’: in 1917. Photograph: AP

At the same time, he is keen to stress that being an actor is nothing like being a soldier. “I hope this isn’t a terribly misjudged thing to say,” he caveats at one point, and, “This is only my extremely cushy version of it.” But he does note some parallels: there is the sense of brotherhood on a film set; the returning home after an experience that nobody else has been through; the sense of pushing yourself beyond normal limits. MacKay’s 1917 character, Schofield, is a quiet soul who bottles up his emotions as a way of forgetting his life back home, and MacKay thinks he did something similar while working on True History Of The Kelly Gang.

“[That film] was the most exhausting physical and emotional time,” he says. “I remember at the end of it thinking, I’ve no energy left. And if anyone asks me about it, I’ll break. It was one of the most profound and joyous experiences. But by the end, I felt very wobbly and vulnerable.”

***

MacKay grew up in Barnes, a villagey suburb of south-west London on the bank of the Thames. His parents (his mother is a costume designer, his father a lighting and stage director) sent him to the independent Harrodian school, which encouraged his love of drama. By the time he was 10, MacKay had his first acting job, and was whisked away to Australia for eight months to play Curly, one of the lost boys in PJ Hogan’s 2003 version of Peter Pan. Back in London, he got on with the business of becoming a normal teenager: “I didn’t really talk about it much,” he shrugs.

‘Even back then, she was a trailblazer’: with Saoirse Ronan in How I Live Now in 2013. Photograph: Rex/Shutterstock

His career hasn’t been all plain sailing. He failed an audition for the Royal Academy of Dramatic Art, but refused to be disheartened: “I decided the next job I got, I was going to actively learn and listen, and look for jobs that could facilitate the learning I would have done there.” And so he picked roles that pushed him to new places. The part he wanted more than anything was that of Edmond in the 2013 postapocalyptic teen drama How I Live Now – because he wanted to learn from its director Kevin Macdonald and then rising star Saoirse Ronan. “I was 20, had spent a year not working, and I knew she was this amazing actress,” he says. “Even back then, she was a trailblazer.”

The two ended up dating while on set (“I suspected what was going on but they kept it very quiet,” Macdonald would later say), which must have made finding the onscreen chemistry a bit easier.

“Yeah,” he says. “I just admire that woman so much. She’s an amazing human being, but that’s all I can say.”

Does he make a habit of falling for his co-stars? “It seems obvious that, if that’s who you’re spending time with, and who you’re getting to know, that’s how we meet everyone,” he deflects. “It’s not a constant through-line but we all meet people some way, either at work or in a pub.”

Is he single at the moment? “I can’t say.”

He is less cautious when it comes to picking his parts. MacKay’s cross-dressing Ned Kelly, for instance, is charged with sexual energy: there’s a homoerotic frisson between him and Nicholas Hoult, who plays a young constable interested in Kelly’s sister; and his relationship with his onscreen mother (played by the director’s wife, Essie Davis) would make Freud blush. As MacKay puts it, “It’s a beautiful, weird oedipal relationship where he’s the little boy to his mum but he’s also her man, and she’s his greatest woman and greatest love.”

‘Making True History was one of the most profound and joyous experiences. At the end of it, I had no energy left.’ Photograph: Linda Brownlee/The Guardian

Two years ago, MacKay encountered a degree of controversy when he played Lutz, a Hitler Youth member who falls in love with a black girl (Amandla Stenberg) imprisoned in a concentration camp, in Amma Asante’s Where Hands Touch. The love story was one element many online commentators were uncomfortable with, although MacKay says he was oblivious because he has no social media presence. Today, he is fiercely loyal to Asante and believes the criticism was misguided. “It suits us to assume that the Nazis weren’t human, that they are a [different] breed, era… But the film is saying: these were humans who did this.”

Playing characters such as Lutz and Kelly has made him “think a little bit harder” about social constructs, he says, specifically ones that have benefited him. “I am recognising that I have never, as a white male, felt like I couldn’t walk into a room,” he says. “It’s a wonderful thing to feel confident. So it’s been a brilliant realisation to be, like, wow, that’s not a feeling that everyone feels? Not everyone feels they could get cast for this? Why, subconsciously, do I feel that confidence – and other people subconsciously feel inferior?”

With Amandla Stenberg in Where Hands Touch in 2018. Photograph: Jo Voets

In an interview last year, MacKay said that he wanted to be more political in his life and work, but his innate caution and fear of offending means he probably won’t usurp Joaquin Phoenix in the wild outburst charts any time soon. When I ask which way he votes, he flushes, looks panicked and, after a pause that seems to hang in the air, puts his hand to his chest and says he would prefer to keep that private. He wants to say the right things about diversity in Hollywood, and equal pay, too, but when we try there are so many false starts – an avalanche of ums and ahs – that watching him try to answer each question feels almost cruel.

“Sorry, I’m not really articulating myself,” he says. “I’m just trying to be careful. I should know the answers to these things, for myself more than anyone.”

And, to be fair, these are issues that many rising stars struggle with: when is it his place to comment? What personal life should he hold back for himself? Can he have an opinion at all, unless he’s certain he can back it up with action? “I want to do everything truthfully and 100%,” he explains at one point, applying the same approach to politics as to his films.

With Dean-Charles Chapman (left) and Sam Mendes at the Golden Globes last month. Photograph: Getty Images

A few weeks after we meet, 1917 wins big at the Baftas, scooping seven awards including best film, best director and best cinematographer for veteran film-maker Roger Deakins. MacKay presents an award with Dean-Charles Chapman, who has been by his side almost constantly over several intense months of publicity-blitzing around the globe. The actors look nervously out at the crowd before MacKay asks if this is still part of Deakins’ continuous take. Unlike most presenters, they get a genuine laugh.

A week later, MacKay is presenting again – this time at the Oscars – and then he is back on a plane to the UK, where he calls me. If he’s exhausted, it doesn’t show. “It was huge,” he enthuses of the Academy Awards. “I grew up watching the results, so to be part of it was overwhelming. Just being in physical proximity, just 10 yards away from Brad Pitt, or Beyoncé, or Scarlett Johansson – and look, there’s Tom Hanks!”

But the memory that will stick in his mind is of reuniting with the cast and crew of 1917 at the Bafta after-party: “When we were making the film, everyone was in their gear all the time – either war costumes or boots and rain macs. So to walk into that room and see a huge number of the crew all done up and smiling was the best thing.”

It sounds as if he’s got a taste for this kind of thing. He laughs and shrugs off the notion, saying that it was a privilege just to be part of a successful film. But I suspect this is MacKay being the polite young man again. And I suspect there will be plenty more plaudits coming his way – probably before he’s managed to grow a proper beard.

● True History Of The Kelly Gang is out now

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