A quick-fire Morecambe and Wise fan with the beard of a Talmudic scholar might seem an unlikely figure to unpick global beliefs, but that is exactly what Larry Charles does in his new documentary Religulous. Expect a supersized controversy for the film, in which Charles, the director of Borat, teams up with another iconoclast, the comedian Bill Maher, for a sardonic look at the world’s religions. Charles will be discussing this eagerly anticipated project at the Britdoc Festival in Oxford this month, where he will be giving the keynote speech.

In the movie, Maher, best known in America for presenting the television satire Politically Incorrect, travels the world interviewing figures from all sides of the belief fence, from Satanists to gay Muslim activists (“That’s a very rare job description”), from Catholics to Jews. George Bush’s Christianity takes a hell of a beating from Maher: “It worries me that people running my country believe in a talking snake.”

It is an intriguing move for one of the most exciting, audacious directors to have made the transition from the small screen to the big. Comedy connoisseurs have admired, respected and chuckled at Charles’s work for more than a decade. He was a writer and director on Seinfeld, which remains one of the highest-rating sitcoms, and followed that with Curb Your Enthusiasm, the bone-dry, boundary-pushing sardonic cult series starring Larry David.

Here is a man who enjoys taking potshots at sacred cows. Charles helped to put masturbation jokes into the mainstream in the famous “master of his domain” episode of Seinfeld, so he clearly has a penchant for trampling on taboos. And you certainly cannot fault his ambitions with Religulous: “The funny will be scary, the scary wildly funny. The crazy will seem sane and the sane crazy. All lines are blurred. All bets are off. We get inside, on top of, behind, and in front of religion.”

He and Maher – a lapsed Catholic who discovered that his mother was Jewish as a teenager – moved in similar comedic circles, sharing ideas and girlfriends: “We had never met, but we had sex with the same women,” Charles says. “Bill was trying to get together a movie about his own spiritual journey, so we saw an opportunity to do an epic about something I’ve always been obsessed with.”

Director and star clearly have issues. Charles grew up in a secular Jewish household and rebelled by wanting to be a rabbi: “I learnt Hebrew and my parents said: ‘Are you out of your mind? Do your bar mitzvah, get the money and get out!’ ” Eventually he rejected the orthodoxy of his teachers, but has been asking philosophical questions ever since, citing the theological thinker Moses Maimonides as an influence, as well as Monty Python. He is shocked that the subject has not really been tackled like this before. “My theory was to take a subject as controversial as religion and see if I can make a movie that people will go to see in a multiplex on a Saturday night when the other options are a Will Ferrell movie or Indiana Jones.”

Imagine a – excuse the pun – cross between Farenheit 9/11, The Life of Brian and Richard Dawkins. Charles himself describes the style as a hybrid, bandying words such as “Brechtian” and “Godardian”. It certainly has strong echoes of auteurs such as Nick Broomfield, with its wobbly camera popping into frame. Charles is a big fan of Broomfield, too: “I loved his Heidi Fleiss and Courtney Love films.”

Religulous also draws on Charles’s improv experience. As with Curb Your Enthusiasm there was no nailed-down script. “I tried to capture a level of spontaneity,” he explains. “With Curb we know where we want to go and then within that we ad lib. Bill and I wrote elaborate outlines and then went out and shot those people. The small crew allowed us to go around and see how lucky we could get.”

Does he feel that he stitched people up? Borat, after all, prompted writs from aggrieved participants. “We just wanted them to say what they had to say, then we pointed out the absurdities of these arbitrary belief systems.” And as for the lawsuits, they fizzled out: “You never hear when they’ve been dropped. None of the suits ever had any merit.” Charles’s favourite interviewees for Religulous were two Catholic priests who surprised him by being reasonable. “One in Rome, one in South Carolina. They were the most enlightened people we spoke to. Very irreverent and understood that the dogma of religion was just that and not to be taken literally.”

Shooting in a theme park in Florida called the Holy Land Experience (“Visit Jerusalem in Orlando!”) was a hoot. “It’s a kitschy, Disneyland version that feels like performance art, complete with its own Jesus and a musical Crucifixion and Resurrection. Then again, the real Jerusalem is pretty kitschy too.” He also filmed radical Muslims in Britain. “The UK has become so tolerant it tolerates intolerance. When I was working on Borat in London I was surprised by how much the city had changed since my previous visit. The old system is collapsing and being replaced by a new one that hasn’t quite been worked out yet.”

At times one cannot help feeling that maybe taking down religion is like shooting fish in a barrel. But the film confirms that any subject can be funny. Charles already proved that in Curb, which addressed terminal disease, racism and 9/11. “No subject is off-limits. If you can find a point of view you can make a legitimate statement.”

So can Religulous change the world? “It is unrealistic to expect Muslims to emerge throwing off their headscarves or Christians pulling down crosses, but the philosopher Daniel Dennett talks about ‘belief in belief’. People know that Jonah being swallowed by a whale is silly, but they believe because it makes them feel good. They are the ones that are the problem, because they give tacit approval to the extremes. I hope the film will speak to those people.”

Britdoc is at Keble College, Oxford (020-7033 2565). July 23-25 2008. www.britdoc.org. Religulous will be released in the autumn

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