Michael Keaton has spoken out about his Catholic upbringing, the value of faith and the danger of institutions ahead of the release of his new film, Spotlight, in the UK.

Keaton plays Boston Globe journalist Walter "Robby" Robinson in the film, which premiered in London on Wednesday. Robinson was the lead journalist in a team that exposed a child sex abuse scandal in the Catholic Church in 2001.

The actor said, "I haven't been Catholic since I was an altar boy... I'm lapsed", but added that he still "drops in" to church and would always defend the value of faith.

Rather than an attack on the Catholic faith, Spotlight is a critique of the institution, he said.

"As much as I hate what's happened in the world based on organised religion and people's alleged faith, I'm a defender and think it's good for people.

"I'm totally cool with my vision of what people call God and I'm good there, but what this movie's about is not religion, but institutions. It's about people who take power and seek power and use that power to disadvantage the disenfranchised and the powerless and it happens in a lot of places, literally all over the world."

Reflecting on a scene when Sacha Pfeiffer, a journalist played by Rachel McAdams, tells her devout grandmother about abuse present in the Church, the 64-year-old shared that his own mother was a committed Catholic.

"My mum went to mass every day and when I think of what (those revelations) would have done to her... I think that's big, it's one thing to do, but crushing someone's faith is another level," he said.

Keaton also shared the hope he found in journalism. "That's what we hope younger people, when they see this film, can get excited about and feel the power."

Walter Robinson and Mike Rezendes, Pulitzer prize-winning journalists from the Boston Globe who inspired Spotlight, have now spoken to the BBC about their investigation.

At the time, Robinson said, the Roman Catholic Church was one of the "most secretive organisations in the world" and a huge challenge to penetrate.

"There was way too much deference paid for way too long to the church," he said. "The cover up that thousands of priests were abusing children in the United States was allowed to continue for too long and finally we did crack the code."

Spotlight is being released in UK cinemas on January 29.