In new horror movie The Secret Of Marrowbone, 26-year-old English actor George MacKay plays Jack – the eldest son of a woman named Rose, who in 1969 returns to Marrowbone, the dilapidated house in rural America where she grew up. Unfortunately, the long trip took a toll on Rose’s poor health, and as she nears death, she makes George promise that he will look after his other siblings until he turns 21 and can become their legal guardian.

However, when an unexpected visitor arrives at the house six months laters, things take a darker turn.

“My parents worked in the theatre before I was born,” explains MacKay of his own background, “which I think creates an image of me growing up in the wings among the pulleys – while on stage some mad cabaret show is going on. It wasn’t quite like that!

“My parents are just very open minded, creative people,” he continues. “I think what I did take for granted and have only appreciated recently is how much theatre I got to see growing up. My parents would take us to plays that were quite adult – never inappropriate, but theatre that wasn’t designed for children. It meant we were often watching plays we didn’t quite understand, but the artistry and the intelligence and emotion slowly seeped in. It set up a foundation and a literacy, I suppose, for theatre and art and acting that now informs the work I want to do.”

I remark that it also exposed him to art and culture he wasn’t aware of, which in the age of marketed ads and “Based on your likes” media, has become a rarity.

“Maybe that’s a modern thing,” considers MacKay, “We’re now more geared towards the quick fix and our own bubbles. Even thinking of Spotify, I’m directed towards so many things because I’m told I will like them – based on other things I like. But that stops us finding things out for ourselves, or exploring beyond our comfort zone.”

Well, it may be controlling his Spotify playlists, but comfort zones definitely aren’t a hallmark of MacKay’s acting career, which is consistently fascinating. His first film role was in PJ’s Hogan’s 2003 version of Peter Pan, where he played a Lost Boy, and he seems to have been drawn to playing odd outcasts ever since.

In How I Live Now, he and Saoirse Ronan (who he reportedly dated) played a group of teenagers trying to survive an apocalyptic disaster; in Captain Fantastic, he played the eldest child of Viggo Mortensen, who raised his kids in the wild to be survivalist philosopher kings with little knowledge of how the real world works; and in The Secret Of Marrowbone, he again plays the eldest sibling trying to protect his family from malevolent forces both human and supernatural.

MacKay’s Jack has endured trauma, and much like his character in Captain Fantastic, lives a life largely sheltered from the outside world. How does he get into the mindset of these intelligent but damaged young men?

“I like to do a lot of preparation, but the type of prep varies,” he explains. “It’s not all about historical research; it can be based in figuring out a character’s past and why they think like they do, and whether they’re aware of their own thought processes. It’s psychology – like I may react to something you say to me, but it’s because I’m being reminded of something that happened to me as a kid, or something hurtful someone said to me ages ago. But I might not realise that that’s why I bite back at you. It’s working out the nuts and bolts of those internal processes and how conscious they are. And with my character in The Secret Of Marrowbone, who has experienced tragedy, that type of nuts and bolt dismantling is vital.”

MacKay’s blend of intuition and analysis is certainly working for his career, and I wonder if there’s something about his education that encouraged this emotional and critical intelligence. As a student, MacKay went to The Harrodian School, which has become something of a factory for young British stars. MacKay puts the success of the school down to its celebration of creativity and the unequivocal support of the students’ passions.

“It wasn’t a drama school,” he says, “they just encouraged us to be individuals, and it was a very safe space to explore who you wanted to be. It was a very open environment.”

Of course, having roles alongside Tim Roth, Chiwetel Ejofor (Tsunami: The Aftermath), Daniel Craig (Defiance) and Clive Owen (The Boys Are Back) at a young age probably didn’t hurt his learning curve either.

“You do learn by osmosis, and in a way, wonderfully taking it for granted!” says MacKay. “I overthink things a lot now! With Daniel Craig, there was definitely a sense of, ‘Oh my god, that’s James Bond!’ But if I was to work with Chiwetel Ejiofor now, I respect him so much as an actor because I know his work. When you’re younger, it’s not that industry craft-based respect for the work that feels as important, it’s just seeing James Bond.”

Now starring yet again as the eldest sibling leading a group of young actors in The Secret Of Marrowbone, what did MacKay learn from those veteran actors about working with children?

“I was really lucky in how I was treated by the adults around me,” he reflects. “Of course, as a child there are certain ways you are protected and certain things you have to do in terms of tutoring etc, but broadly people just treated me as an equal, as much as possible. People asked me how my day was just as George – not in a patronising ‘How are you doing, little fella?’ way! It’s not about leadership, it’s about equality, and I hope I help cultivate that.”
The Secret Of Marrowbone is in cinemas now.