Four Lions, Chris Morris, 101 mins, (15)

Is anything off-limits for comedy? Chris Morris, of 'Brass Eye' fame, pushes the boundaries again with a story about a inept terror plot on London

(Picselect )

Television satirist Chris Morris has made his first cinema feature, and it's an irreverent farce about suicide bombers. Hah – nearly had you believing me.

After all, his series Brass Eye hoodwinked various celebs into warning of the perils of "Cake" – an entirely "made-up drug" – then had them swallow stories about paedophiles sharing their DNA structure with crustaceans. Combining strategic lucidity and a sulphurous imagination, Morris is a master at skewering hysteria and gullibility. But honestly, did you really believe he'd make a knockabout comedy about British mujahedin?

Well, honestly, he has: Four Lions tackles the most authentically taboo topic aired in British cinema in living memory. Morris, co-writing with Jesse Armstrong and Sam Bain, goes about it with his usual savage levity, yet with absolute seriousness too: the film emerged from three years of research. And its key finding is that suicide bombers are basically credulous buffoons – like most of us, when scrutinised through the Morris optic.

Inheriting from the long tradition of comedy about inept anarchists with fizzing bombs, Four Lions depicts its terrorist cell as marginally less capable than Warner Bros' hapless Coyote. The first we see of Morris's anti-heroes, a group of British jihadis in a northern town that's apparently Sheffield, they're making a terrible hash of a martyrdom video. Afterwards one of them, Omar (Riz Ahmed), shows his wife the shoddy material he has to edit: "These are the out-takes – the bloopers."

Morris's characters are inept but well-meaning amateurs – if you can be well-meaning while plotting to take innocent lives. Faisal (Adeel Akhtar) is an earnest duffer with a flair for bomb-making, with a plan to strap explosive to crows: it works fine, if you want to combust a crow. Omar's sidekick Waj (Kayvan Novak) is a naïf who sees martyrdom in terms of jumping to the head of the queue at Alton Towers. And Barry (Nigel Lindsay), a white convert to Islam, is the most fanatical of all. A hardliner of the sort that will grab at whatever hardline is going, he's a fount of febrile free-associative rhetoric: "Jews invented spark plugs to control global traffic." It's Barry who proposes that the cell's target should be a mosque, because Islam has gone soft: "We've got women talking back; we've got string instruments; it's the End of Days."

It's a smart move by Morris to have a sort of straight man in the gang – a nearly rational grown-up, more or less – and to cast the likeable Riz Ahmed, an actor of easy nuance. Omar is an ordinary bloke out of his depth, who fails to see the contradictions of everything he thinks he believes in. Despite his jihadi fervour, he enjoys a secular-style home life, and an easy-going and tender relationship with his wife Sofia (Preeya Kalidas). The more we see of them, the more outrageous it is that Omar wants to throw everything away, and that Sofia buys into his delusion. She encourages him to go ahead with his plan: after all, it's about her man living his dream.

If there's a key theme in Four Lions, it's contradiction. Trying to keep Waj in line for their mission, Omar spins him a garbled piece of sophistry about listening to his heart, not his head, then ends up having to persuade him that that the organs in question have somehow changed places. Omar plans to bring down Americanised Western culture, "the Church of McDonald's", yet he worships it as much as anyone. He sells the ideal of martyrdom to his admiring son – in scenes at once tender and hair-raising – by telling him bedtime stories, a jihadi re-rewrite of The Lion King.

There are some extremely dark moments, especially when the gang attempts to bomb the London Marathon and the inevitable begins to happen. Yet the film is not unrelentingly black. Some of its most effective scenes arise from tenderness, or a warped version of it. There's an extraordinary male bonding moment between Omar and Waj, a declaration of mutual buddyish devotion – but they're actually promising that each wouldn't hesitate to kill the other in a pinch. Beneath the rhetoric, these would-be killers are just confused mates with a shared vision; you might see Four Lions as a fundamentalist Full Monty.

This perverse tenderness gives the film a painful clarity, especially as concerns Omar: unlike his comrades, he has a chance to choose sanity, but disastrously rejects it. Morris does not just deride the bombers, but humanises them; some may see that as either a cop-out or an outrage, but it makes Four Lions all the more challenging and morally serious.

In the end, Four Lions isn't as confrontationally jaw-dropping as expected, flagging just when the intensity should be mounting to intolerable levels. And arguably, it's not quite as funny as it might have been: Morris has toned down his surrealism, although there are a few of his trademark linguistic salads, lines like "You tomatoed your friend and killed the special needs donkey". Still, this bold venture shows that Morris dares laugh where others only splutter with nervous embarrassment: Four Lions is a comedy that puts the error in terror.

Next Week:

Jonathan Romney heads to Cannes. Will Ridley Scott's festival opener Robin Hood hit its target, or just go twang?