“I’ll wash my mouth out with soap.” Anthony Boyle is apologising for the egregious misstep of mistaking my Canadian accent for an American one. It’s about as bad as if I were to mistake him for an Englishman, I joke.

“Exactly! It’s the worst!”

In all fairness, we were discussing the States. Just before the lockdown, Boyle was in New York City with his brother, for the premiere of The Plot Against America – an HBO miniseries based on Philip Roth’s novel of the same name. In it, alongside the likes of John Turturro and Winona Ryder, Boyle played a member of a Jewish family in an alternate version of American history, one where they endure the political rise of Charles Lindbergh and fascism in the United States during World War II.

“Everyone started talking about Covid potentially shutting down the city,” the actor recalls. “My brother and I thought, ‘Instead of going back to London, we’ll go back to Dad’s house in Belfast. This whole Covid thing’s going to last a week – tops’. We moved out about ten years ago, so we thought it’d be nice to just see the family for a little while.”

Needless to say, it didn’t quite pan out that way.

“We were there for a fucking year,” he deadpans. “And we have very thin walls, between my brother and I. I could hear him cough... But he didn’t have Covid!”

Now safely back in his own space in London, the 26-year-old looks on his sojourn in Belfast with fondness.

“My sister’s 16, and we got to hang out in a different way when I went back,” he notes. “We would watch Friends together. I’d never watched it, and quickly became obsessed with Ross," he laughs. "Drinking whiskey late into the day, saying, ‘find me a Ross-heavy episode!’”

The nature of an actor’s life is that they must go where the work is, but Boyle misses New York.

“I love the energy of that city,” he enthuses. “I love how late it stays open, that you go out and think that you’re going to have one kind of night, and end up experiencing a completely different one. I love that you meet people from all walks of life.

“I love that you can be in Manhattan and then go to Brooklyn and feel like you’re in a different country. It’s just an incredible city.”

The first time Boyle was living in The Big Apple – close to Times Square, “right in the belly of the beast,” he says in his Northern drawl – he was there for the Broadway run of Harry Potter And The Cursed Child.

“New Yorkers would say to me, ‘Why do you want to be in such a touristy area?’ and I was like, ‘Because I am a fucking tourist!’”

Tourist though he may have been, Boyle can consider himself well and truly indoctrinated into the Broadway world now. He was nominated for a Tony Award for his role as Scorpius Malfoy – the misfit child of Draco, who enters into an unlikely friendship with the son of Harry Potter and emerges as the play’s unlikely hero.

The part also earned him an Olivier Award in the UK, although Boyle isn’t sure those accolades change much for actors when they’re given out.

“I wasn’t handed a great fountain of knowledge about acting when I was given the award,” he reflects. “I won the Olivier and then booked off a week with my then-girlfriend to go on a holiday. I was like, ‘I don’t want to even know where we’re going, just surprise me.’ We ended up going on a cruise. I’d never been on one, and we were the youngest people there by about 50 years,” he says, emphatically adding: “no, really, someone died – on the fucking cruise!

“When I got back, I had this notion in my head: ‘This is your first moment as an Olivier Award-winning actor. You have to give an award-winning performance’. I went on and gave a bad or an average performance, and realised that none of it matters, it’s all just a load of shit. It was a good learning curve to experience early on, it made me really relaxed about the whole thing. It’s a good lesson – that no one really cares. Maybe it did get me into rooms I wouldn’t have gotten into before, but I’m not sure.”

Still, it’s a long way to have gone for a young boy from Belfast, where acting wasn’t – still isn’t – the ‘done thing’, despite the success of Northern Irish actors like Jamie Dornan and Conor MacNeill.

“Conor gave me my first short film,” Boyle says warmly. “There’s a place in Belfast called Andytown, and I call him ‘The Andytown Oscar Wilde’. I don’t know if he likes that, but there you go.”

The short in question, The Party, is set in the 1970s and sees Boyle’s character being snuck in drag from one side of the city to the other to see his friends. Expertly written and beautifully shot, it was nominated for a BAFTA for Best Short Film back in 2017.

“I suppose I was always quietly encouraged by my parents to pursue acting,” Boyle recalls. “There wasn’t a great amount of theatre being made, at least not when I was growing up. The majority of people are boxers. It’s certainly not something that feels like an option. I had a real determination that I was going to be an actor.

“Teachers would often say, ‘You need something to fall back on’, which I completely get now, when I look back at it. They were just trying to do their jobs. But I felt such anger about it when I was younger, I was always like, ‘What do you mean? I have to be an actor’.”

It’s a good thing he pursued it, judging by his latest turn in Danny Boy. The BBC drama, which examines the human cost of war – is based on the true story of Brian Wood, an ex-British Army soldier who was subjected to accusations of war crimes in the Al-Sweady Inquiry, after he returned from Iraq.

Boyle is perfect for the role, classically handsome in a boyish way, with sad, wide eyes. He plays into Brian’s extreme vulnerability with a gentleness that shines, despite scenes where Wood has to deal with intense PTSD, lack of proper counselling, and a fraught relationship with his father.

“I found the vulnerability more interesting than the explosiveness of it all,” Boyle says. “When you speak to Brian in real life, there’s a real vulnerability there. Especially when he spoke about being a Dad, or his son.”

Playing a real person must come with its unique challenges.

“I’d speak to Brian about his own experience, which I was trying to go from,” says Boyle. “You end up doing a lot of Googling, watching documentaries about people who suffer from PTSD. Finding things you can draw on, so that you have something when someone says ‘action’, rather than making it up on the spot.

“My job is not to think about the macro of it all,” he maintains. “It’s to focus on the micro, to try to play it as truthfully as possible and live each moment. And to not think about honouring people or offending them – just to accurately portray another human being. When you start to play into, ‘This group of people watching are going to think this’, whether it be positive or negative, you can get tripped up.”

This is a conversation Boyle had with his co-star, Toby Jones – who plays Phil Shiner, the former human rights solicitor who was struck off for misconduct during the Inquiry – although not until after the project was wrapped.

“Toby and I got to work with each other again on the film that I did afterwards. Two weeks after I wrapped Danny Boy, I was standing in a courtyard in Glasgow with Toby, and all the tension that was drawn up during Danny Boy got to be released when we had these big scenes.

“I can’t speak for Toby, but I think he’d have a similar viewpoint in the sense that he wasn’t thinking – or couldn’t think – about the wider aspects. That he had to play it for Phil Shiner, and play it as truthfully as possible.”

Boyle studied at the Royal Welsh College of Music and Drama in Cardiff, and has been fortunate enough to have worked with some of the most revered actors in the world – Jones among them. Despite formal training and his well of experience, he remains completely unpretentious about the craft.

“My own view on acting is: learn your lines, show up, don’t be a dick to anybody,” he says bluntly. “Do whatever you want to do, as long as you aren’t affecting other people, you know? Still say ‘Thank you’ to the person who picks you up in the morning, and the people who are giving you lunch. Whatever falls in between that – being a normal fucking human being in a workplace – do it.”

He also prefers the theatre to film.

“The stage is an actors’ medium,” says Boyle. “You’re the editor, the director – you control the piece. It’s like being in a church and delivering a sermon, there’s something reverential about it. Sometimes with film, it can seem technical, small, and mechanical.”

But fret not – Boyle won’t permanently forego the screen for eight shows a week.

“Well, there’s more money in TV and film,” he laughs. “It’s definitely a cushier lifestyle!”

• Danny Boy is on BBC 2 now.