Daniel Kokotajlo is, he admits, feeling a little proud. And he has a right to be. His debut film Apostasy, which he wrote and directed, is riding on a wave of positive reviews from film festivals around the world. It’s a brilliant drama following the lives of three female Jehovah’s Witnesses, and exploring with devastating honesty what happens when fundamentalist faith collides with real life.

“It took a long time to make,” Kokotajlo says. “And I felt a lot of pressure to tell the story in a balanced way and get it right.”

Although speaking from his home in London, Kokotajlo, now 37, has retained his broad accent from his upbringing in Tameside, and Apostasy (the name means formal abandonment of a religion) is filmed in and around areas Kokotajlo grew up. Using this setting was important, he says, not just because he knew it well.

“The way the Witnesses work as a community in the north was interesting to talk about, right down to the little details – for example, the way that they are learning to speak Urdu to go out to Asian communities to try and convert them.”

It’s those small details that give the film its rich sense of authenticity, which has been so applauded by critics. You can tell that Kokotajlo has inside knowledge of this world.

“I’d decided that I didn’t really believe anymore but it was hard to get out of it.”

Born in Tameside Hospital, Ashton-under-Lyne. Kokotajlo grew up in a “brick poor” household. He was eight when his mother met two “kind older people” who told her about the Witnesses, and she joined the church. She went on to bring not only her three children into the religion with her, but to recruit other members of the extended family.

They were attracted to the appeal of the church’s message, says Kokotajlo. “It’s very appealing for someone to think that one day all of humankind will be equal, we will no longer have to worry about money and we all get to live forever in a perfect world. There’s something very comforting as well in the black and whiteness of it, the idea that you have the key to the universe and that you have all the answers, and you actually know more than people in a higher social class. You know better than the doctors and the experts.”

But for the young Kokotajlo, it was tough. “It meant that we were no longer celebrating Christmas and birthdays and all that stuff. And I suddenly started to become more of an outsider at school and in social situations.”

Siobhan Finneran, Sacha Parkinson and Molly Wright in Apostasy, shot in Greater Manchester

The film focuses on Ivanna, brilliantly portrayed by Siobhan Finneran, and her two daughters, Luisa (Sacha Parkinson) and her devout younger sister Alex (Molly Wright). Luisa falls pregnant by an “outsider” and when she refuses to marry him and bring him to the Witness meetings she is “disfellowed”, cast out of the congregation. The elders (the male leaders of the congregation) then encourage Ivanna and Alex to avoid contact with Luisa, despite her pregnancy and poor financial situation, causing a terrible rift in the family.

Aside from seeing how his own mother and other female members of the family had been treated in the church, Kokotajlo was also inspired to put women at the centre of the drama on hearing a secret recording of a reinstatement meeting, where someone attempts to re-join the church.

“[It was] a young woman and she was talking to three elders. She’d just had a baby and not spoken to her mum for several months and she had been doing her hardest to reinstate herself, but these elders weren’t having it. They were horrible to her, abusive and didn’t believe a word she said. She just broke down. And when I heard it, it brought me to tears and I thought we need to shed some light on what goes on.”

In the film, Luisa starts to have her faith eroded when she attends college and meets outsiders. Kokotajlo himself began to drift away from the Witnesses when he started to study for his BA in textiles at Manchester Met.

“I was exposed to worldly things. There were temptations that they warn you about and that’s why they discourage you from going on to higher education.”

By that point he was hiding the fact that he was a Witness from his friends at university, coming up with excuses not to attend birthdays and Christmas parties – celebrations that Witnesses see as pagan in origin.

“I’d already decided that I didn’t really believe anymore so I was mentally out [of the church] but physically I was still going. It was hard to get out of it.”

His move away from the church was gradual. He “drifted away” and eventually ended up at Westminster University, where he studied for an MA in screenwriting, having completed his degree and made a living from his fine art, music, and filming greyhound races at Manchester’s Bellevue dog track.

But unlike Luisa, Kokotajlo was never disfellowed. “They’re still hoping I might come back one day. You have to formally disassociate yourself or do something that will get you disfellowed, like committing some sort of sin.”

He has spoken briefly about the film to family members who are still Witnesses, but doubts they will ever see the film.

“It’s a bit too close to the bone for them. It depends how curious they are.” Indeed, while ex-Witnesses have been turning up to previews and connecting with the film, he’s not sure that many, if any, current Witnesses will come, although he hopes they will. “They might be advised by the elders not to see it.”

If they did go and see it, they would hopefully agree that Apostasy is a balanced film. Watching it, you see the painful anguish that Ivanna suffers when faced with the choice of either renouncing all that she believes, or providing love and care to her own daughters.

“I know people might watch this film and think Ivanna is just a crackpot, but hopefully you start to see things through her eyes and understand what’s beguiling about a religion like this.”

Despite the positive things he recognises about religion – “faith does help people” – it’s the dogma that is a problem, he says, such as the Witnesses’ approach to blood transfusions, which they believe should be refused, an issue also explored in the film.

“I used to carry around the alternative medical card in my wallet which would advise doctors what to do if there was an emergency,” he explains. “It was a concern even as an 11-year-old kid. We used to talk about it in the Kingdom Hall. What would you really do if you had to take a blood transfusion? It was scary even when I was a believer. But they play it down, they don’t talk about it in the same way that outsiders do, they discredit the doctors, they talk about how blood is not the only option, that it’s the cheap option and there are alternative medicines out there which are more successful.”

What are the after-effects of such an upbringing? “I’m always looking for answers. Maybe it was in music at first, and then film – that became my religion in a way. I took it very seriously. It was a sort of purpose in life. I guess I’m always doing that – trying to look for a reason.”

And where does he stand with faith now? Does he ever worry that when Armageddon comes he won’t be among those who make it to the “new system”, the paradise that only Witnesses will get to enjoy?

Kokotajlo laughs. “No. Maybe in my darkest hour I might start to feel like that. But I don’t believe in that any more. The more you read about it, the more you see where stories from the Bible come from. I’m still learning and reading about science. That’s where I am at in my life right now, learning about the world and how it works, I’m not ready to think about spiritual things yet.”

Apostasy is in cinemas now