David Mackenzie has never shied from the uncomfortable and complex. Having announced his arrival with the critically acclaimed Young Adam, Mackenzie went on to direct Hallam Foe, Asylum and Perfect Sense.

The director’s latest movie, Starred Up, is a hardboiled prison drama.

“It’s odd, but I found making a prison film very liberating!” laughs the director. “There’s something interesting about playing with the limitations of the form – you’ve got cells and corridors and observation blocks and people. That’s kind of it. You get to focus on the environment and the dynamics of emotion. In confined spaces everything feels explosive.”

The film was scripted by former prison therapist Jonathan Asser, who wrote a semi-autobiographical character into the screenplay. Though lead actor Jack O’Connell is incredible as a rage-fuelled young offender, Mackenzie seems equally drawn to the privileged therapist, the complexities of class and emotion he represents.

“He’s a trustafarian, essentially, and has this inner need to give back. There’s something interesting in that... There’s also the idea the character has been repressing his rage because it’s what society expects. It’s clear he’s not a do-gooder. He has the potential to be as... dangerous as the inmates. Which is something in all of us, to a certain degree.”

Workshopping the script with former inmates, Mackenzie says some of the film’s tensest sequences were inspired by real events.

“In the therapy sessions, there are scenes where the dynamic reverses and you see the group of inmates trying to calm the therapist down. That’s because we did some sessions while rehearsing which got very heavy because Jonathan grew very intense, and had to be calmed down. And that was interesting – watching anger build, then de-escalate. It never gradually dissipates, it’s always a barbed deflation. That was such an intriguing dynamic to me. I asked Jonathan if we could use that interaction on screen.”

Mackenzie agrees there’s a thread of self-examination in all of his work.

“I got into a lot of trouble during my teens,” he remarks bluntly. “There was a sense of being in freefall and exploring all these emotions but not being able to understand or control them. It’s also the one time you really are allowed to take these emotions to the extreme. Adults are expected to effortlessly cope – and many of us can’t.”

Starred Up is set to become one of his most acclaimed movies to date.

“I like the idea of searching for truth in a straighter, less poetic way than in the past.... I enjoyed the grittiness and the realism of this film. I’ll stick with this method of finding true emotion, until I get bored and try something else!”

Starred Up is in cinemas from March 21