In tough times for the human spirit, clever comedians become more reliable than clever politicians. Comedians just have more truths to tell and they are usually less afraid of what they might lose by telling them. Politicians often have intelligence but only the very rare ones have a commensurate moral vision, which is what Saul Bellow was talking about when he noted that “a great deal of intelligence can be invested in ignorance when the need for illusion is deep”. So, in these glory days of humbug and false witness and the horrors of belief, might we call forth the comic writers and film-makers to do their work?

Thankfully, in Britain, we can, if the talent happens to be as perky, searching and fit-for-purpose as that of writer David Baddiel and director Josh Appignanesi. What they have done with The Infidel is to make a laugh-along moral drama that brings a great big dose of enlivening absurdity and comic brilliance to a taboo subject, the hostility between British Muslims and Jews. The film sets out with the kind of notion that used to make Woody Allen, at his early best, such a life-enhancer, showing us what happens when a man filled with self-certainty suddenly has no self and no idea how to live.

Gallery: The Infidel premiere

The results are cracking, joyful and instructive, and the film is already certain, in my mind at least, to be the summer’s funniest film. It has such large things to say, but is a total laugh and a real turn-up for the books.

Mahmud Nasir (Omid Djalili) is one of those family guys who sits around the house wearing a football top. He is good at being a father and less good at being a Muslim, though he would probably go to the wall for both. You wouldn’t set the kettle by his strict observances but he appears to know who he is, despite his liking for old videos of a Gary Numan-like New Romantic Eighties pop star who reminds him of his youth.

Anyway, Mahmud is a likeable, expansive sort of bloke, the sort of ageing lad you reckon gets all his pleasure from knowing what he likes. Imagine, then, the splendid horror — the vista of comic potential — that opens up when Mahmud suddenly discovers that he is not a son of Islam at all but an adopted son whose birth certificate tells him he was once called Solly Shimshillewitz.

As I say, Woody Allen would love this. But so too would have Billy Wilder and Ernest Lubitsch. The scene is set for the most lovely combination of personal identity crisis and cultural stereotyping, leaving you hollering with recognition. Nasir’s son is hoping to marry the beautiful daughter of a local, much-feared, unjovial, fatwa-friendly imam, a man who feels that our hero might not be quite Muslim enough. (If only he knew.) There are no spoilers here but let me just say the ensuing comedy is thrilling on several fronts — the joy of reason unseating prejudice, yes; the smile of anarchy spreading mayhem unto dogma, yes; but also the thrill of watching haphazard intelligence take a powerful stand against well organised stupidity.

The film is brave in that way but to be offended by it you would have to dislike movies, and would have to feel that comedy is a regrettable form of insubordination. Watching Djalili’s excellent face, following his dismay, believing in his human trouble, you could not fail to see that, in the oldest traditions of movie-making, humanness and comedy are the only antidotes to hatred. The film communicates this with precise energy, and causes you to have a nice time while you’re being led out of the dark.

Baddiel has provided character and verbal dynamism throughout, in a biting script. He has the gift of being able, very naturally, to make you laugh at the pieties of the Jews and the Muslims equally, throwing gags and thoughts into the mix in his signature way. With The Infidel, Appignanesi jumps, in one beautifully executed move, to join the front rank of new British directors. His timing is perfect, his feel for the rhythm of moral action is bracing, and I hope he goes on to make a ton of interesting movies.

The Infidel gets itself into hot water, as every real comedy should, but I’m happy to report that it’s the warmth you remember, a feeling of gentle revelation about the absurdity of building one’s identity on religion.

Omid Djalili, in the title part, is pure gold. As many a Jewish comic might have said, there’s nothing funnier than a crisis of the soul, and Djalili communicates Mahmud’s trouble first with a consternated expression, then with a palette of outrage and love. The film should be a breakout one for this guy: he is immensely funny and true as he struggles to be Jewish, and a ferocious everyman by the end. Richard Schiff, familiar as Toby Ziegler, White House director of communications in The West Wing, pulls off another blissful, complicated character in Lenny, a Jewish cab driver who lives across the street from our hero.

Lenny begins in a state of hostility towards the Islamic Mahmud but ends up taking responsibility for his neighbour’s Jewish education. Schiff does all this with amiable patience and with low expectations. He is the unlikely buddy, the unexpected conscience of the piece, and in each of his scenes he adds to the comic lustre of this very winning film.