But let's be clear about this from the start - Religulous reserves the full onslaught of its firepower for Christianity, and in particular the homespun American variety. Around ten minutes of its 90-minute running time is given over to Islam, less still to Judaism. Buddhism and Hinduism are not even mentioned. Instead, we are treated to a series of interviews and encounters with assorted fruitcakes, fraudsters and the simply not very bright, who mostly prove no match for Maher's professional schtick or indeed, one suspects, his clever editing team.

The governing principles of filming seem to have been set by the Louis Theroux and Ruby Wax school of factual programming. Find the softest targets you can, set them up and go in for the kill. Occasionally, this is entertaining in an embarrassing kind of way, such as when Maher interviews a spectacularly thick Evangelical Democratic congressman. But mostly the result is repetitive and demoralising. What possible point is served by interviewing - at some length - an actor who plays the part of Jesus in some tacky Holy Land theme park in Middle America? Is he going to talk himself out of a presumably much-needed gig? Why stroll into a tiny truckers' chapel on the edge of some highway and get chummy with the down-home guys, who are perfectly welcoming until the penny finally drops that they're being used as stooges? It's always a bad sign when film-makers determined to make a point resort to filming Speakers Corner in Hyde Park but on their global travels Maher and Charles and their crew leave no such cliché unturned.

Maher - the child of a Jew and a Catholic - is occasionally funny with his wry asides but the relentlessness of the overall approach is counterproductive. Something is wrong if, like me, you are an agnostic with atheistic tendencies and you find yourself rooting for the other side. But more important than this is the disturbing cultural trend of which this film is a part. You do not have to be Christian, or religious at all, to see that the sole reason why movies such as this - or Dawkins's books, or indeed the endless media discussion about the causing of religious offence - now exist, is the rise of a radical, politicised Islam. Out of fear, or misplaced sensitivity, or both, this fact cannot be admitted. Instead, we turn our guns on ourselves. If we rid ourselves of this superstitious nonsense, the reasoning goes, then the world will be a hell of a lot safer for all mankind. Maher makes no mention of the Enlightenment. There is no reference of how Church and State were separated. Footage of imams calling for the death of Jews is intercut with George W. Bush praying. The effect, obviously intentional, is to leave one with the impression that the trucker in his cabin is, in his way, as misguided and dangerous as the suicide-bomber. We are no better than them.