While Borat saw Larry Charles travel across the US with Sacha Baron Cohen's hapless Kazakh TV reporter, Religulous sees the director taking in a range of religious sites - Jerusalem, Vatican City and Florida's Holy Land Experience - with comedian Bill Maher as he skewers religion.

Maher and Baron Cohen's methods may be different but, says Charles, 'they are both fearless performers. Bill just uses his own persona and Sacha uses his characters.'

Premiered at the Toronto International Film Festival, Religulous opens in the US through Lionsgate on October 3.

'After Borat I was very interested in revisiting the idea of religion and seeing if I could make some kind of a comedy about it,' Charles explains. 'I was called in to meet with Bill and he was talking about the same thing. So we synthesised our points of view. We met at just the right time - we're both middle-aged white guys who don't give a shit, who aren't afraid to cover this topic.'

As with Borat the shoot was relatively footloose. 'We had, in both cases, such a small footprint that we could do that,' Charles explains. And this approach had real benefits - while doing a scene with a Vatican priest, for example, the production was taken inside the Vatican. 'Nobody checked our ID or our credentials,' Charles says. 'Suddenly we were in and the priest goes, 'There's the Pope's apartment right there.''

Considering his background as a writer, Charles is remarkably open to surprises while shooting. 'One of the things I had to get over as a writer was that sense of control,' he says. 'As a director I try to have as little control as possible because I want to be surprised. A lot of that came from working on Seinfeld, which was a very controlled environment. I want something to happen that's not on the page.'

Borat managed to combine edginess with commercial appeal and Charles says part of the point of Religulous is to take a very difficult subject and see if it can compete commercially. 'I want it to compete with The Dark Knight,' he says straight-faced. 'That's the audacity of something like that. That's part of the theory - can you make a movie about religion, about such a polarising, serious, controversial subject, and make it entertaining enough that people looking for a movie on Saturday go, 'Oh, there's The Dark Knight, but this seems good also. This is going to be entertaining.''