'A life of prison, addiction was just one step away from me'

When he was growing up in east London in the Nineties, David Jonsson would be told stories by his mother about the youngsters she was seeing each day. She was a police officer for the Met, and would come home, sigh and look intently at her son. "I don't know which way some of these boys are going," she'd tell him. "Please, don't be like that." Jonsson, his voice so soft and careful that he seems 32 going on 60, knew what his mother was doing. "She was full of love and care and empathy, but also frustration. She was trying to help."

Today, Jonsson is one of Britain's busiest young actors - the star of the romantic comedy Rye Lane and the Stephen King adaptation The Long Walk, and last year the recipient of the Bafta Rising Star Award. But he knows a path was laid out for him that wasn't as rosy. "Honestly, a life of prison and addiction was just one step away from me."

Jonsson was just 16 when he was expelled from school in London's Newham for fighting and truancy, leading him to enrol in a new school in Hammersmith. It was there that he discovered a love of acting, and a dream of a career that gave him purpose and drive. He'd later train at the National Youth Theatre and at Rada, and venture far from the kind of trajectory his mother was afraid of. "I was so close to that [other life], that it was almost tangible," he says. We're in a hotel in London, Jonsson hunched at a breakfast table and wrapping his arms around himself. He is swaddled in a dark-red hoodie, a stud in his ear and a watch shining on his wrist. Life has taken a massive turn.

He's talking about what might have been because his new film, he says, is the "closest to home" that he's ever played as an actor. In Wasteman, he stars as Taylor, a heroin-addicted father who's spent 13 years in jail for selling drugs to a teenage boy who later overdosed - it was a terrible mistake, revealed in spurts over the course of the film, that resulted in Taylor receiving a manslaughter conviction. As we meet him, he's told he's up for parole, but it's an opportunity endangered by the arrival of a new cellmate, Tom Blyth's volatile, drug-dealing Dee. Whereas Blyth is a tightly wound coil forever on the cusp of unfurling, Jonsson is fragile and wounded, if hardened by years of regret. It's a carefully modulated performance, and arguably his finest to date.

Jonsson had been attached to Wasteman for several years, but financing only materialised three weeks before production began, meaning his physical preparation had to be fast. "And I knew I wanted him to be struggling with addiction and to feel as if something had been taken from him, so he needed to be thin," he recalls. He lost two stone, reducing his body mass by eating just 700 calories a day. Meanwhile, Blyth was going the opposite direction, bulking up to play a character as violent as he is physically imposing. At the end of filming, they were able to drop any sense of antagonism. "He goes, 'Mate, we all good? Should we go to the pub?'" Jonsson laughs.

The craziest thing about being a young Black actor is a lot of times you're having to break new ground. And it's a really unnecessary pressure that you don't actually want

Wasteman is gritty and complex, and eager to spark conversation. I ask Jonsson if he thinks Taylor should have been imprisoned, considering his age at the time of the incident and the specifics of the crime. "I don't know if I have an answer to that," he says. "Because he committed a crime, and a crime that affected a lot of people. But I also believe in second chances, even third chances." The prison system is complicated, he adds. "At its core, it's a rehabilitation system. Or at least it's meant to rehabilitate. So it's kind of beside the point whether you think someone should be there or not. Because they're meant to be being helped."

I'm curious about whether his mum has watched the film, I tell him, considering the work she used to do. Jonsson winces. "I don't really like her watching anything of mine. I'm way too embarrassed. I'm sure she'll find her way to this one and tell me that I was being naughty." He laughs. "I know she wants to watch because she's proud. But I'm also, like... mum, look away."

It's probably a given that Jonsson's mum hasn't seen him in Industry, the bonking'n'banking drama that first propelled him to fame. He played Gus, the Old Etonian with political ambitions, but only for two series — by its third he was gone, under slightly opaque circumstances. Why did he leave it behind? "I always try to compare this job to being a plumber or a builder, because those are the people I grew up around," he says. "I want this job to be as normal and regular and working-class as that. But, you know, it's not." He laughs again.