John Sweeney knows he may always be remembered for a single moment. While filming an investigation of the Church of Scientology for the BBC current-affairs programme Panorama, in 2007, the journalist felt he was being obstructed, harassed and spied on.

This provoked a feeling he describes as "unendurable pressure" until, during a terse exchange with a Scientology spokesman, Sweeney cracked and lost his temper. The footage from the documentary, Scientology and Me, went viral around the world.

“For a time I felt hunted,” he says, explaining how the sense of intrusion lingered after the show’s production. “People turned up at our wedding. They called to my mother-in-law’s home, in Devon, asking questions. People came to our house, making fake deliveries to our neighbours. It was uncomfortable, dark and scary. No question. You don’t fall out with the Church of Scientology and do it lightly.”

Although Sweeney routinely expresses regret whenever the outburst is mentioned – “People in the public eye should be civil to those they disagree with. It’s part of the engine oil of democracy” – he says a curious thing has happened in the years since. Former Scientologists have come to cite that incident as emblematic of Scientology in the 21st century.

“That image is what the church does to people,” he says. “I used to be a war reporter. I’ve been to many, many bad places in the world, and I had never been through anything like that.”

Undeterred, Sweeney later began work on a book called The Church of Fear: Inside the Weird World of Scientology, drawing from his experiences making the original Panorama programme and its 2010 follow-up, The Secrets of Scientology. It's the reason he'll be speaking at Scientology: Enough Is Enough, a two-day conference in Dublin next weekend.

The event’s organisers claim it will “reveal the abusive conditions, financial exploitation . . . and broken families that lie behind the Scientology organisation’s veneer of religiosity”.

Controversial subjects

Sweeney has a record of tackling controversial subjects, having also written books on Britain’s arming of Iraq, Romania under Nicolae Ceausescu and tyranny in North Korea. But finding an outlet for an exposé of Scientology proved difficult.

Media coverage surrounding the divorce of Tom Cruise and Katie Holmes, Sweeney says, seemed to suggest that Scientology's reputation for aggressively stifling analysis had diminished. But the publishing industry still appeared daunted by the prospect of lawsuits.

“Nobody would touch the book,” says Sweeney. “No major publisher in Britain dared to buy it. Eventually my agent said, ‘I’ll publish it,’ and we’ve managed to sell 25,000 copies through Kindle and print-on-demand. But you’re not going to find it on any bookshelf. The problem with the church is that it generates fear and incapacitates people who would normally report on them.”

In 2013 the UK publication of Going Clear: Scientology, Hollywood, and the Prison of Belief, by the Pulitzer Prize-winning journalist Lawrence Wright, was cancelled on legal advice. The book became a bestseller in the US and Canada before being adapted into a forthcoming documentary by the Oscar-winning film-maker Alex Gibney.

So what’s the fascination? What draws people towards refuted claims about a religious organisation that sees itself as a force for good? Sweeney says that in a world where we’re always on the lookout for something that may be bigger or more meaningful, the esoteric theology and celebrity endorsements behind Scientology can prove alluring.

Or perhaps people naturally become intrigued, he suggests, when former members tend to characterise Scientology as “something like the Coca-Cola corporation or a brainwashing cult or a weird zombie state or all three mixed into each other” rather than as a religion.

Attempts to reach the Dublin branch of Scientology for comment on this article were unsuccessful.

Sweeney has become friends with seven former high-ranking Scientologists, including Mike Rinder, former head of its Office of Special Affairs, whose job it was to denounce the claims being made in the original Panorama broadcast.

That some of these former members still believe in the teachings of Scientology's founder, the science-fiction writer L Ron Hubbard, has no bearing on their friendship. Sweeney's main issue has always been that everybody, whether inside or outside the organisation, should feel free to express doubt or pose questions without being dismissed as detractors engaging in discriminatory behaviour.

“People have a right to believe in whatever they want to believe in, and I defend that,” he says. “But along with a right to belief there is also the right to be a sceptic, to be mocked, to scrutinise and to criticise. You have a right to believe in whatever you want, but other people have a right to say, ‘This is bonkers.’

“What we’re seeing now with the jihadis is a tendency to say, ‘This is what I believe in, and you can’t criticise it.’ That’s a frightening thing. Within that you get to a state where you close your mind down. I think if you believe in a God, a good and all-powerful being, then He can put up with a little bit of criticism. That should be accepted: the freedom to believe, the freedom to criticise. Those two rights must exist equally.”

Given the value that Sweeney places on transparency, he finds it appalling that any mention of Scientology seems to be ruled off limits when the likes of Tom Cruise appear on high-profile platforms such as talkshows.

“What’s wrong with that is there are many people out there who are vulnerable and who, young fans in particular, associate Tom Cruise with a jet-setting lifestyle,” he says. “And behind that is something called Scientology. Well, this thing isn’t good in my experience. But if you’re so proud to be a member of it, why can’t we ask some questions? In the modern world we should be able to exercise scrutiny.”

Scientology: Enough Is Enough begins on Friday at Filmbase, in Temple Bar, Dublin; see exscientologistsireland.org