'I filmed a movie entirely inside a prison cell'

Scottish actor Bryan Larkin says the intense experience of shooting his latest film is not one he would like to repeat in real life.

Jailbroken was filmed entirely within the confines of a prison cell and Larkin says the psychological toll of the shoot makes it "the best anti-prison film you could probably ever get".

The 52-year-old actor, who grew up in East Kilbride, plays Joe, a violent inmate who, just days before his release, receives a chilling phone call informing him that his ex-wife and son have been kidnapped.

Armed only with a smuggled mobile phone, he faces a race against time to save them while locked up in his jail cell.

Larkin, who has previously appeared in major Hollywood productions such as London Has Fallen opposite Gerard Butler, is returning to his roots for this independent film, set in Scotland.

The movie, which had its world premiere at the Glasgow Film Festival on Thursday night, also stars veteran Scottish actor David Hayman as a smugly sadistic prison guard.

Larkin says both his own character and Hayman's "represent a gritty reality for audiences".

He says they are characters that viewers might recognise as people they've met coming out of a pub or at a taxi rank arguing.

The actor says they are the kind of people you are highly aware of but might not want to live next door to.

However, Larkin says he wanted to show the humanity beneath Joe's tough criminal exterior.

"You're going to get to see this dinosaur, this violent, toxic man," he says.

But even people who are really depraved have something they love, he says.

For Joe, that motivation is saving "a son that has no memory of him".

To get into character, Larkin got involved with director Vasily Chuprina and writer Raymond Friel three months before shooting began.

Together, they worked on ways to try to highlight Joe's hidden vulnerabilities.

Once production began, the physical reality of the claustrophobic set quickly took a psychological toll, Larkin says.

He says the intense environment led him to become "highly territorial".

"There were times when I was in there, it felt like my house," Larkin says.

He admits that the confined shoot made it "hard to get out of character because you start to feel like that's your domain, that's your space".

This blurred the lines between actor and character, leading him to question anyone entering the cell, he says.

"I felt anytime anybody comes in there, I was like, 'have you got a right to? no, don't move that'."

Another significant hurdle was performing with a telephone as one of the other main characters in much of the film.

Fortunately, the production hired two actors to deliver the dialogue live from off-set, rather than relying on pre-recorded lines.

Larkin says this completely altered his acting process.

"You really have to listen even more closely than you would if you were acting with someone opposite you," he said.

He added that the set-up required a "shift in your concentration from outward to really kind of inward and making the words affect you more".

Jailbroken marks the feature-length debut for the director.

To visually represent the protagonist's mental breakdown without making the single-room setting feel static, Chuprina says that he purposefully changed the camera lenses as the story progressed.

The director says he initially used wide lenses, which highlighted that Joe was "distracted, he's not a likable person".

As Joe's mental state deteriorates and he becomes more exposed and child-like, the camera was physically moved closer to Larkin using longer lenses.

"It's not only claustrophobic for the character, but of course it's claustrophobic for the viewers," Chuprina says.

Larkin echoed this, saying the visual goal was to make the audience feel as if they are "sharing that prison cell" and eventually "sitting on Joe's shoulder" as he breaks down.

By locking the audience in a cell with a desperate man, the film tries to strip away traditional action to focus entirely on human psychology and the consequences of a life of crime, Larkin says.

He hopes the harrowing journey leaves a lasting impression on viewers.

"If you're even thinking about doing something that could potentially land you there, watch Jailbroken before you do," he warns.