The mere mention of new Channel 4 romantic thriller Trespasses causes Tom Cullen to start shaking his head and giggling. That’s how the acclaimed Welsh actor displays his pride at being involved in the adaptation of Louise Kennedy’s prize-winning debut novel, which tells the story of young Catholic schoolteacher Cushla (Lola Petticrew), who falls in love with a married Protestant barrister Michael (Cullen) during the height of the Northern Ireland conflict in the 1970s.

“I actually couldn’t believe that I was even being asked to audition. It felt so beyond my reach and capabilities as an actor. It felt like the role should go to a movie star. It terrified me,” says Cullen.

It’s a little surprising to hear such insecurity and self-doubt from the 40-year-old when you consider the magnetism he has brought to his roles. Whether it was his breakout part as the reserved Russell in 2011’s romantic drama Weekend, the charming Viscount Gillingham in Downton Abbey, or ruthless criminal mastermind John Palmer in The Gold, Cullen has an innate ability to make his characters feel real, complex, and captivating.

When it came to Trespasses, though, Cullen’s main concern was perfecting a Northern Irish accent. “I sent off this audition tape doing a diabolical Northern Irish accent. It was like a horror movie,” he self-deprecatingly insists. Regardless, Trespasses’ director Dawn Shadforth still wanted to sit down and discuss the show with Cullen. “We did this read-through together, just the two of us. We did it nearly a dozen times. I still knew the accent wasn’t good enough.”

Despite Cullen’s concerns, Shadforth had seen enough. She pushed for Cullen to star opposite Petticrew, Gillian Anderson, Martin McCann, and Gerard McCarthy in the four-part series, expecting him to have the accent honed in time for filming.

“That’s when the absolute dread set in,” admits Cullen. “The cultural specificity of an accent is essential to a character. I knew I had so much responsibility and couldn’t let the people of Belfast down. I went into panic and survival mode. I didn’t lose that worry until the day we wrapped filming.” As someone who has watched many a performer butcher Welsh accents, he knew how meticulously scrutinised his Northern Irish vocals would be. He also knew that the only way to get it right was to put the work in.

Cullen worked alongside Belfast-based dialect coach Jude McSpadden, who he says needed the patience of a saint for the pace he was perfecting the voice. “I did hours and hours and hours and hours of work. I did dialect on the beach, at my sister’s wedding, every night before bed, in the gym.” The biggest helping hand Cullen got, though, came from a fellow actor – but one he has never met. “I listened to Jamie Dornan’s Desert Island Discs hundreds of times. I’ve never met him but what a great guy. I feel like I know him now.”

All of his hard work and dedication eventually paid off. At the read-through in Belfast, which was, unsurprisingly, mostly made up of people born and bred in the city, he convinced co-star McCann that he was a local, too. “He told me that was one of the best Belfast accents he’d ever heard. That calmed me down a little bit, but I was still panicking about the rest of the performance.”

That said, being terrified about a performance appears to be Cullen’s acting sweet spot. “If you’re not shitting yourself, you’re not working hard enough,” he emphatically explains. “It’s hard to talk about this stuff without sounding like a wanker, but you have to go through it; you have to step out of the way and allow the character to flow through.”

Cullen has his parents to thank for his love of acting. They were both artists who performed at a small theatre company in his hometown of Llandrindod Wells. “Acting got its claws into me like an infection,” he poetically declares. After his parents divorced, Cullen moved to Cardiff with his mother. A somewhat delinquent teenager, Cullen describes himself as an “angry young man,” much in the mould of the working-class characters portrayed by Richard Burton, Albert Finney, and Richard Harris in the classic British New Wave movies of the early 1960s.

The idea of acting moved further and further away until, aged 21, Cullen had to confront the person he was becoming. “I remember waking up, looking in the mirror, and I didn’t recognise myself. The next day I applied to the Central School of Speech and Drama in London.” He was accepted but only lasted a year, as he continued to “put up a lot of armour and the angry young man was difficult to get rid of.” Back in Cardiff, he applied to the Royal Welsh College of Music and Drama, where head of acting, Dave Bond, saw something in the raw, precocious, but undoubtedly skilled Cullen.

“That was the perfect place for me. Dave gave me the space to iron out my kinks and my tricky personality. I was often in his office in trouble, but he had a lot of patience. He just saw something in me. I’m so grateful to him. I wouldn’t be here today without him.”

While Cullen clearly had to soften certain parts of his personality, he didn’t want to completely get rid of his edge and emotional baggage. Instead, he’s opted to explore his complexities through the characters he portrayed. His hope is that viewers see themselves on-screen and are either able to overcome their own issues or seek the necessary help.

“Suicide is the biggest killer of men under the age of 50. It needs to be looked at and talked about. Why are men so angry? Why can’t men communicate? Why do we still struggle to talk about our emotions? Life hasn’t always been easy for me. I want to play characters who overcome adversities. Who redeem themselves. Who figure out who they are. I’m just a sucker for a complex male discovering his vulnerability.”

Trespasses is available to stream on Channel 4 from 9 November 2025.

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