TESTIFY! Bill Maher, HBO's libertarian wiseacre, and Larry Charles, director of Borat, have made a film about the ever inflammatory subject of religious belief.

Religulousis repeatedly disrespectful towards the Abrahamic faiths (relax, Shintoists and snake handlers, you get off lightly). It focuses to an unfair extent on soft targets, such as a Florida-based loon who claims to be the reborn Jesus. It cynically juxtaposes hilarious clips from dated religious films with shots of trusting, devout interviewees.

What else? Copying a technique used by cornered fanatics on internet forums, the film-makers hone in on the smallest grammatical or syntactical error as a way of making their opponents seem stupid. (A Christian senator says “literary” when he means “literally”. What a moron!)

In short, Religulousis biased, contemptuous, ad hominem and snide. I thought it was hilarious.

Maher, son of a Jewish mother and an Irish Catholic father, makes an effort to present the film as a journey of discovery. At various points, we encounter the comic driving along the freeway, musing upon the undesirability of blind faith or the inconsistencies of a particular belief system. To make sure we get the message, the film-makers then play a section of The Who's The Seekerat us.

This is all prime baloney, of course. Maher, a famously devout agnostic, is not open to persuasion or enlightenment on this subject. Closer to Borat's unfettered satire than the disingenuous hand- wringing of Michael Moore's films, Religulousis merely an excuse for our host to construct jokes around the absurdities of organised supernaturalism.

As things turn out, the witticisms are so consistently amusing that even the faithful may find themselves cracking the odd smile. Indeed, the loudest laughter at the expense of religion comes from a senior Catholic priest. When the affable Father Reginald Foster, the Vatican’s chief Latinist, hears Maher suggest that the Bible be taken literally, he actually rocks with uncontrollable hilarity.

At moments like this – attend also Bill’s meeting with the Vatican’s chief astronomer, another wise bird – Maher’s certain uncertainty appears to crumble ever so slightly. Maybe there is room for questioning minds in organised religion.

It doesn’t last. St Peter’s is barely beneath the horizon before Maher is back into his stride. That final monologue takes him to a hill in the Holy Land, where his argument on behalf of doubt (though sound in its moral and logical foundations) becomes increasingly declamatory, until it turns into something a little like a sermon. I thought that’s what we were trying to get away from, Bill.

Directed by Larry Charles 15A cert, Light House, Dublin, 101 min★★★