OF course, we start with the Academy Awards. So, George, I say, I have to ask. What’s the Oscar story you’ve been telling everyone since you came home?

In a car travelling through London between a radio station and a trip to the shops, George MacKay hums and haws and then starts talking about America’s alternative first couple.

“We wound up at the Jay-Z party on the Sunday night,” he tells me, “just dancing away in a room full of people you recognised from music videos over the years. Which was mad, but great fun.”

Did you speak to Jay-Z, George? Did you ask Beyonce for a dance? “No, I didn’t. I saw them across the room. Just to know they were in the same room and getting down was pretty cool.”

George MacKay has arrived at the point in his life where he can be in a room with superstars. He’s not quite one himself but who’s to say that this time next year he won't be.

MacKay is 27, made his debut as an actor at the age of 11 in the 2003 version of Peter Pan and has been slowly but very surely working his way up to being a leading actor, with roles in Proclaimers' jukebox musical Sunshine on Leith, Captain Fantastic and, of course, Pride, in which he played the young gay boy who was the quiet, still centre of a story about the gay community supporting the miners during the bitter strike of the mid-1980s.

This year, though, you could say, he has arrived. Playing the lead in Sam Mendes’s bravura war film 1917, with its long fluid takes giving the impression it’s all one continuous shot, has meant he has spent the last few months in promo-land, turning up on TV chat shows and radio shows and talking to journalists and dressing up for the Baftas, where 1917 won Best Film, and, of course, the Oscars, which turns out to have been a mere hors d’oeuvre for a proper Grammy-winner’s after show party.

The film has rather taken over his life for the last year. “It was November 2018 that we first started rehearsing and we’ve been with it sort of constantly since,” MacKay says. “Since October I’ve been on the road promoting it.

“It’s a much bigger film than I’ve done before. When films I’ve been in have done well it’s been more gradual. There hasn’t been any mass reaction to it, whereas this has been extraordinary.”

Whatever you make of 1917 – emotional rollercoaster or impressive technical achievement and not much more – there’s no question that it has raised MacKay’s profile exponentially.

Is he getting recognised in the street now? “A couple of times, yeah. It’s nice. Everyone’s been really lovely. Anyone who has said anything has been touched by the film, so it’s been a positive experience.”

The promo is nearly at an end now, though. Our conversation is squeezed into a day that will otherwise be spent doing “homework” for his next project, Wolf, about a boy who think that he’s a … Well, you can probably work it out.

Even in the briefest of conversations MacKay, the son of a costume designer mum and an Australian stage manager dad, presents as a well-spoken, well-mannered young man who’s possibly had a public-school education (he has, The Harrodian in south-west London). Mostly well-spoken, I should perhaps say. There are times when, explaining an idea, he gets tangled up in so many qualifiers that he begins to sound like a Hugh Grant character, albeit less sweary. And less inclined to quote David Cassidy lyrics.

Still, that only makes his performance in his latest film, True History of The Kelly Gang, all the more impressive. In Justin Kurzel’s new take on the life of Ned Kelly, bushranger, outlaw, police killer and authentic Aussie legend, MacKay burns down the screen as Ned. In the film MacKay’s a vision of muscle and bared torso (the film critic Peter Bradshaw describes his physique in the movie “as fiercely muscular and taut as a Vesalian anatomy illustration,” which is pretty accurate). That’s when he’s not wearing a dress, of course.

As it happens, Kurzel’s brutal, ultra-masculine movie which also stars Russell Crowe and Nicholas Hoult and is based on Peter Carey’s novel, was made before MacKay turned up to film 1917. And if anything, MacKay says, it was making True History ... that prepared him for taking on Lance Corporal Schofield.

Playing, or rather prepping to play, Ned Kelly pushed him out of his comfort zone, he says. Before filming even began he spent three months in the outback chopping wood, learning to ride horses, “kind of going bush a little bit,” he explains. “It’s so far from where I’m from.”

Could he have coped with that kind of life? “I would like to think that I could cope, but I just wouldn’t be me if I was there. Simple things. I didn’t realise how soft my hands were. You know, I go to the gym a couple of times a week. I think I’m in relative shape. I’m young.”

But it turns out none of that had prepared him for digging a ditch or building a fence, it seems. “I can lift a dumb bell, but I can’t build a fence. I can’t dig a hole. Saddles are heavy. That was an important learning.”

Because to be Ned he had to have that knowledge. “As much as Ned in this film is full of vulnerability and is very damaged, he also has a very quiet and powerful confidence because he is so able. The hardship of his life has made him very able in a lot of ways. Which makes him primally confident, I guess.”

That was what MacKay had to become.

To understand his character the actor steeped himself in Australian history. Irish history too, given that Ned Kelly’s father had been born in Tipperary. MacKay travelled there to talk to a historian about the Kellys' background.

“He questioned me. ‘What do you know about Irish history?’ I was embarrassed to say, ‘not much,’” MacKay admits. “We spent a whole morning together in Tipperary going back to when the Normans came. Fascinating stuff.”

None of this is directly relevant to the story, he says (although the film is very aware of the tensions that existed in 19th-century Australia between the English policemen and the Irish citizens). But it gave him a better handle on the character and even the history of his father’s country.

“To look at the big stuff you have to concentrate on the small,” he argues, “and this one man grappling with his identity and where he’s from feels pretty relevant to the country of Australia as we know it now.”

I’ve read, I tell him, that during rehearsals his director told him and the other actors – Earl Cave (Nick’s son), who plays Ned Kelly’s brother Dan, Sean Keenan and Louis Hewison – who make up the Kelly gang to form a band and write some songs. It’s true, he confirms.

“We had four weeks’ proper rehearsals with all the team there and Justin said, ‘I see the Kelly gang as a punk band. I want to make the film in the spirit of these men rather than adhere to the history, and I reckon they are a bunch of angry, confused, ambitious young men trying to put their mark down. I think they are a bunch of punks.’”

It’s one interpretation. Kurzel took it a bit further when he told the four of them, they were going to play a gig in Melbourne in less than a month. And they had to write songs to perform.

“And so, we did,” MacKay says. “And it was the most amazing experience. He said, ‘I want you listening to each other in a different way. You’ve got to be aware of each other. You’ve got to be in rhythm with each other and that comes from music.’”

As a result, in July 2018, an unknown punk band called Fleshlight (possibly best not to Google it) turned up at the Gasometer in Melbourne wearing women’s dresses and days-old, drunkenly applied make-up and made a proper racket.

As an experiment in team building, MacKay suggests, it totally worked. “The experience of putting together 10 songs in three weeks and playing it in a bar gave us that swagger. We then walked onto set like, ‘Yeah, come on then.’”

Were the songs any good? “Well, two of them are in the film. We liked them. I think we are going to try and release them. One of the bands that was a big reference point was Eddy Current Suppression Ring. One of the fellows from that band polished up a track the other day and passed them onto a label he knows.”

Future punk star or not, MacKay is very good as Ned Kelly and it’s a performance that has the force of revelation about it. It’s wild and on the edge of derangement and couldn’t really be much further from the very English, very polite suppression of emotion that he essays in, say, Pride.

“Ned really stretched me,” MacKay admits, “emotionally and physically. I know we weren’t digging rocks, but I went further than I’d ever gone in any sense, outside of family and relationships.”

It was, he suggests, a totally immersive experience. “It’s the job where I’ve blurred most and that’s an exciting and sometimes quite scary feeling. In a way it’s a beautiful feeling. It’s quite … Not damaging to do … It costs for a time to give over to something completely.”

Well, I ask, what are those costs? Are we talking about exhaustion? Exhaustion, yes, he says, but more than that. “I went past a lot of where I thought I could. I don’t know what that teaches you about yourself. It just teaches you that you can go a lot further than you ever thought you could.”

And, in turn, that was then key when it came to make 1917, he says. “I auditioned for 1917 soon after I got back from Ned,” he says. He says he remembers thinking, “I’ve got the energy to do this.”

MacKay goes back to talking about Ned Kelly once more. “There is so much family stuff entwined in the film. It has a lot to do with looking to your roots to find out who you are. And that was a big thing, going back to understand my dad’s past in Australia.

“I remember speaking to my mum and dad, saying, ‘There is so much I want to tell you but if I talk about it I will break and I don’t know if I can put myself back together and so I’m just going to wait ’til I’m home.

“When you go to the end of yourself it teaches you what you circle back to. It’s almost as if you’re elastic. The harder you tug one way the faster you ping back. It clarified the things that I ping back to.”

What those things are he doesn’t, maybe can’t, articulate. I think it’s to do with home, with family, with love. “There wasn’t a massive revelation,” he does say. “It’s the simplicity of things that you truly understand the weight of when you’ve been as far away from them as you’ve ever been.”

Was there a day on set where he thought, “I can’t do this?”

“It got close, but in a way that’s what is exciting. It’s rare when you feel like, ‘I don’t know if I can carry on.’”

But, he’s quick to add, his director was there for him during all this. “Justin really looked after us. He is an amazing director because he understands that the work is good when it is close to those extremes. But he also understands the responsibility of taking someone there.

“It’s easy to do that carelessly, but Justin and Sam in 1917 … There’s so much love there. There’s a feeling of human love in all its forms running through both of those films. That’s a result of the directors crafting a place that’s safe to really push yourself.”

Making True History … and 1917, he says, has made him begin to dream big. He loved the three-dimensional quality of both films. It’s made him think that when he’s older he might like to write and direct, “because I’ve just been so thrilled by having a greater understanding of my role and everyone’s role in the making of things.”

For now, though, he’s happy enough being an actor. Who knows? Maybe this time next year people will be asking Beyonce if she talked to George MacKay?

True History of the Kelly Gang is now on general release.