THERE are moments – though not many – when Lewis MacDougall still sounds like a 14 year-old boy. Like the story he tells when, over the summer, he was on his way to his local drama group, The Drama Studio, in Edinburgh. “Right by there, there was a massive big camera on a crane and it was filming through a window,” he exclaims. “I could see in the window and it was Danny Boyle! They were filming the second one!” He is, of course, talking T2 – the much-awaited sequel to Trainspotting.

He’s hardly alone in his giddy excitement, seeing the director behind one of the greatest Scottish films ever made. But this behind-the-scenes sneak peak is nothing new because MacDougall – Scotland’s latest screen star – is already past that proverbial velvet rope. After being directed by Joe Wright in last year’s J.M. Barrie spin Pan in a supporting role as Nibs, he now takes the lead in A Monster Calls, alongside the more seasoned Felicity Jones and Liam Neeson.

When we meet, in the Mayfair Hotel restaurant, it’s the day after the movie’s premiere at the London Film Festival. MacDougall is accompanied by his father William, a retired banker originally from Glasgow. But when we sit to chat, William politely disappears, leaving us to it. MacDougall is more than capable of articulating his thoughts without any parental coaxing; he was just 12 when he shot A Monster Calls, though any inexperience is impossible to detect.

Based on the novel by Patrick Ness, MacDougall plays Conor, a young schoolboy living in northern Britain. Bullied at school, and with a father (Toby Kebbell) who is largely absent, he is also facing the loss of his terminally ill mother (Felicity Jones). Ill-equipped to cope with such emotional upheaval, he begins to visualise the huge tree outside his window coming alive – a manifestation of his feelings of guilt and grief towards his mother.

Directed by J.A. Bayona, the Spanish filmmaker behind the devastating tsunami drama The Impossible, the screening I attended had people in floods of tears – a common cathartic response to a film that explores death in a touchingly profound but simple way. “I think fantasy and fairytales have an important part in making sense of reality,” MacDougall says. “Conor seeing the monster is trying to make sense of life and what life will be like.”

Perhaps MacDougall was doing the same. In 2013, he lost his own mother, Fiona, after a long illness. Understandably, being on set brought the trauma of this back. “It was a bit close to home,” he admits. It’s not hard to see why MacDougall gives such a stunning performance: raw emotion simply pours from him in the scenes between he and the "monster" (vividly played by Neeson, via motion capture technology).

Without professional training, MacDougall exposed himself like an open wound. He talks about getting “stressed” on set, “having to reach the levels of emotion” required. “Getting to that place can be very difficult. Sometimes, forcing yourself to get to the place where you’re actually crying…that was the bit that was stressful. But to be honest, I almost found getting stressed contributed to me being able to get tears out.”

What about bullying – has he ever experienced that? That too is a pertinent topic in the film. “I’ve thankfully never been bullied myself – it’s a horrible thing,” he says. “I can definitely say I’ve seen it at school. But Conor’s situation is different. He almost wants to be bullied. He feels like he should be punished for what he thinks. The monster ends up teaching him…wishing for the end of pain is the most human wish of all.”

Sitting in front of me, a white T-shirt with red and blue flashes on it encasing his thin frame, MacDougall looks just like your next Xbox-playing, Rangers-supporting teen. But statements like this blindside you; MacDougall’s experiences on set and in life have left him mature beyond his years. “I know this role will stay with me for the rest of my career,” he adds. “You don’t get roles like this come around often for a child my age.”

Intriguingly, he’s already spent time with Tom Holland, the young English actor who is now playing Spider-Man – and previously starred in Bayona’s The Impossible. “He actually visited the set [of A Monster Calls]. If you look carefully in the credits, he got a credit for being a monster stand-in on set for one day. He’s somebody I really admire. It can be hard to make the transition from being a child actor to an adult one.”

Facing his school exams in a year-and-a-half, MacDougall knows he has to focus on that; beyond that, he’s trying to keep his options open. “I’m interested in other stuff – academically,” he says. “Like politics. I pay close attention to that. I’ve got other interests that I may or may not try and pursue. But this is going well and I enjoy it. Whether I do go to a drama course or whether I don’t, hopefully it’ll keep going.”

Already MacDougall has bagged two further roles. In Boundaries, an American road movie, Vera Farmiga and he play mother and son, driving up the West Coast to meet his pot-dealing grandfather (Christopher Plummer). Then there’s The Belly of a Whale, playing a misfit teenager who becomes embroiled in a plot to rob an amusement arcade. But what about playing a superhero – like Tom Holland? He smiles. “I wouldn’t mind being Superman or Batman.”

A Monster Calls opens on January 1.