The actor Michael Socha and his friends spent their teenage years in Derby getting drunk, stabbed and arrested. Now, in their mid-30s, they go on ­"sober walks". He auditioned for his ­latest role, in the second series of the BBC legal thriller Showtrial, the day before setting off on a ­20-day trek following the Camino de ­Santiago pilgrimage trail to north-western Spain, and heard he had won the part while en route. "It helped the walking process," he says. "I walked a little bit faster and with more determination. I wanted to go back and get on with the job."

Socha has a long list of screen credits to his name since his debut, aged 17, as Harvey, the bully with a blond quiff, in Shane Meadows's 2006 film This Is England. Since then, he has appeared in three TV spin-offs of the movie and portrayed a werewolf in Being Human, the extraterrestrial love interest of Michaela Coel in The Aliens and a desperate father in Chernobyl.

But he insists that he was still taken aback to be offered the role of Justin Mitchell, a cocky policeman accused of murdering a climate-change activist, in Showtrial. "I couldn't believe it. I'm still in the mind-frame that I'm a working-class kid from Derby that shouldn't be playing this sort of a character," he says in a photographic studio in the centre of the city he still calls home.

When he arrives, chewing gum and apologising for his creased white T-shirt, he tells the photographer he is "s--- at having my picture taken". How is he at interviews, I ask. "I'm f---ing s---e at that, too." It is far from the truth. He does not demur from a single question, and answers openly - not raising his large, mournful eyes from the floor until he has completed his ­expletive-laden, but expansive answers.

The new series of Showtrial - related to the first only by themes - covers a plethora of hot-button issues, from environmental direct action to toxic masculinity and insidious police WhatsApp groups. Socha is known for doing up to six months' preparation - "All sorts of mad things" - for a job. In advance of his lead role as a 1700s coin counterfeiter in the 2023 BBC Two drama The Gallows Pole, he lived and worked on a farm, while learning the patois of 18th-century weavers.

Here, without the luxury of time, he had to make do with grilling both the writer, Ben Richards, and the director, Julia Ford, about the character's intentions across ­various scenes, and posing questions such as "Does he really love his missus?"

The 36-year-old was already quite familiar with the police. As a child, "Me and mine were all getting nicked," he says breezily. He would prefer to leave the specifics "to the imagination", but points out of the window to the magistrates' court just across the road. "If I weren't in there, my friends were." Although today he loves the people, the history and the vistas of the city, when he was growing up, "I thought this place was a s---hole. It just seemed like everywhere was a battlefield."

At Saint Benedict school, he was "a naughty boy", who left with just three GCSEs, destined for a life on a building site. His only salvation was drama, thanks to the persistence of his teacher, Mrs Urquhart-Hughes, and his mum, Kathleen, driving him the 30 minutes to Nottingham's Central Junior Television Workshop, which had already made stars of Samantha Morton and Vicky McClure (Showtrial co-star Joe Dempsie is another alumnus). His sister, Lauren Socha, would ­follow in his footsteps, winning a Bafta TV Award at 20 for Misfits.

How long before he stopped being, in his own words, "a little ­s---"? "Not that far off, to be honest with you. I think by my early 20s I'd stopped being arrested, anyway." At 18, he moved to a flat-share in London's Seven Sisters, convinced he was "going to be making the big bucks down in the big smoke". Instead, he found himself trying his damnedest to get casting directors to turn the page on his "chav phase".

He ditched his Nike baseball cap and trainers. "And I thought, I've got to put a pair of Converse [trainers] on and wear some skinny jeans and AllSaints T-shirts," he says with a chuckle. The new wardrobe proved a fruitless investment. "Because my head wasn't any different. I was still that lad... just wearing AllSaints."

Socha had already observed that his newfound actor friends inhabited an environment that was "more lucrative and safer". But he somehow always found himself trapped between the two. "I'd go to London and be quite arty, I suppose, and cultured. And then I'd come back to Derby and just get straight back to the s---." This reached its nadir when he had three television acting jobs lined up, after a stop-off back home.

Following closing time at the Half Moon pub in Derby, he and his mates walked down to Asda to get a bottle of brandy, and then, "I ended up getting stabbed in the head. I had to work on all these f---ing jobs with a face that was ballooned."

After I express my horror, he reassures me: "Well, it didn't go through my skull. An alter­cation happened between my friend and another lad, and then I just remember waking up with one of my friends crying above me. It was here," he says - pointing to a bump on his forehead - "that I got hit with a dog chain, and here" - gesturing above his ear - "I think it was a Stanley blade. My other mate got stabbed in the leg." Returning to set, he made up a story about getting into a fight on a train and had the make-up ladies cover up the "massive f---ing gaps in my head".

He credits acting for his ability to show the vulnerability his character in Showtrial finds impossible: "I'm always playing a version of myself that I'm not allowed to express." He also commends the support of his friends - who all have nicknames such as Badger and Bison: "I'm not scared to say I'm scared, ever, really." He is still pals with one of the guys who also got attacked. They are both now tee­total and "we climb mountains, like every f---ing millennial does".

He was reminded of his erstwhile sloppy attitude to work when he asked his agent how he could get into a new TV hit, Game of Thrones. As he tells it, she replied: "Oh, you did have an opportunity to audition, but you said you didn't like mythical dragon things." "You div," he says of himself with a shrug.

He is equally forthcoming when I ask about his father, who left the family when Socha was very young and died when he was 15. "It was an alcohol-related heart attack, or something like that. He drank himself to death, I think. He used to drink them Tennent's Super f---ing strong cans."

But he prefers to dwell on his good fortune, citing the Nottingham Workshop kids who didn't get the chance that he did: "I think I was in the right place at the right time. And maybe luck didn't ­sprinkle on a lot of people from Workshop. They were some of the best actors I've ever seen."

His social-worker mother - just as in the days when she was ferrying him to rehearsals - still "finds it all a bit intimidating, like I do". Socha - who doesn't like to discuss his private life, but lives between his ­eldest child in Derby and his other two children in South London - adds: "My mum's never been impressed by a film set. I think she's just happy that I'm a good father to my kids."

He steers clear of "utterly difficult" red-carpet events and industry networking. But unlike a decade ago, when his "two worlds were separate and I had to decide whether I wanted to dance in that one or this one, now I know who I am. And I don't have to dance in any f---ing world. I just do my own thing."

Showtrial begins on October 6 on BBC One