Four Lions (15)

It doesn't gnaw at the funny bone

The sleep of reason begets monsters, as Goya's famous title ran. In Chris Morris's satiric worldview reason hasn't so much gone to sleep as fallen into a coma, but the monsters Goya envisaged – ignorance and folly – are no less terrifying. They just come in different guises nowadays. From his early work in radio right through to his goading outrages on the box, Brass Eye and Blue Jam, Morris has always identified his principal target as gullibility, one of ignorance's lowly cousins. If, for instance, you can persuade politicians and opinion-makers of the dangers of a nonexistent drug – perhaps you remember "cake" – then what other nonsense might you get people to swallow?

Never one to shirk the comic possibilities of hysteria, Morris addresses, in his debut as writer-director, the incendiary subject of modern jihadism. He has said that the film is based on three years of research into the terrorist mindset and methods: the surprise is that he discovered not systematic ruthlessness, but varying levels of incompetence and farce. "People go to training camps in the wrong clothes, forget how to make bombs, fight with each other, and then fight again over who just won the fight." So it is that the wannabe mujahedeen of Four Lions tend to behave more like the Three Stooges.

Their base is a nondescript flat in the heart of a northern city. Feesal (Adeel Akhtar) is a bomb-maker who can't run a suicide mission at the moment because his Dad's got sick and "started eating newspaper". Instead, he's trying to train crows to fly bombs through windows. Waj (Kayvan Novak) is a gormless tagalong who appears to imagine that being a soldier is just like a theme-park ride. Barry (Nigel Lindsay) is a white Muslim convert of such moronic extremism that he regards even buying a Jaffa orange as tantamount to backing a Jewish conspiracy. The cell's leader, and by some distance the sanest and most sympathetic character, is Omar (Riz Ahmed), who listens to his confederates' bickering with a kind of stoical weariness: when they argue the toss between bombing a mosque and bombing Boots, the chemist, you can tell from his face that he knows he'd be better off on his own.

It's also clear that Omar, the only family man among them, is the most dangerous member of the gang. His wife, an NHS nurse, and his young son both know of his jihadist mission, and egg him on. It's a subtle paradox of the film that Omar, the true believer, reserves his deepest scorn for his devout brother, who openly preaches Islam yet abjures the practice of violence. But farce undoes even Omar's best-laid plans. Hoping to win terrorist credentials at a training camp in Pakistan, he fatally mistakes the business end of a rocket-launcher and has to flee, leaving calamity in his wake. Back home, he finds his leadership of the cell challenged by Barry, whose big idea now is to radicalise Muslim moderates, because "Islam is crackin' up, bro'". The film sets up these tensions carefully, and by degrees shifts the tone of playful mockery towards something darker and more despairing. The character of Omar is key to this, for he alone realises the mismatch between their globalist ambition and the practical and intellectual limitations that shackle them.

In the early stages Four Lions invokes the spirit of Ealing Comedy, as the gang, transporting explosives to their safe house, try to avoid blowing themselves to atoms. Later, as the threat of violence looms, Morris switches his focus to the security services and their efforts to track the bombers; here, too, mishap reigns, and competence gets it in the neck. Yet while you may understand what the film is getting at, there comes a point when you have to acknowledge that there's something amiss with it. No matter how astute and topical and considered a satire might be, it exists essentially to make you laugh. And I'm sorry to say that, for all its intelligence, I didn't find it remotely funny. Not because it would have felt in "bad taste" to laugh, or because its tragic elements overrode its comic ones, but because the jokes didn't ring true.

The script, by Morris and his co-writers Jesse Armstrong and Sam Bain (of the brilliant Peep Show), plays it very, very broad. They expose the shambolic nature of DIY terrorism as if to reassure us: behold this bunch of toerags with their dreams of martyrdom. But however dunderheaded Morris found actual jihadists to be, they could not be quite so pitiful as this lot. At times the film-makers don't seem sure how stupid their terrorists ought to be: ubermilitant Barry in one scene punches himself in the face to win "an argument", but later he is seen on a panel discussion of Islamophobia. Waj is so clueless as to be almost mentally impaired, but when he says "I'm thick as fudge" the line sounds clunky. He's not bright enough to know how thick he is. The fate of these would-be soldiers does, in the end, achieve a grotesque sort of pathos, and in Riz Ahmed's portrait of an angry Omar there is a tragic sense of waste. Morris wants us to provoke us into thinking more deeply about issues of race and belief and national security. It is an honourable aim. But it still left me wishing he'd provoked us into laughter.