Two IRA activists, Chris (Cillian Murphy) and Frank (Michael Smiley), are escorted to a gun deal with the flamboyant South African arms dealer Vernon (Sharlto Copley). A misunderstanding ensues, shots are fired in a panic, and the deal collapses into an extended and deadly shoot-out in a disused warehouse.

English director Ben Wheatley has developed a hugely impressive resume of feature films, including the folk horrors Kill List and A Field in England, and the satirical High Rise. Free Fire sees him attempt a new style of bleakly comedic film: a rolling, no-holds-barred 90-minute gunfight. It boasts a funny screenplay, a slick and effective pace, and a fantastically talented cast of actors.

The film is essentially one long sequence that runs in real time. It begins with the best of intentions: Chris and Frank want to buy some guns, and Vernon wants to sell them. What neither party realises is that a driver on the IRA side, Stevo (Sam Riley), was assaulted by a henchman on Vernon’s side, Harry (Jack Reynor), after violently abusing Harry’s cousin. Their personal conflict gets out of hand, shots are fired, and explosive mayhem ensues. Shortly afterwards a third party of snipers turn up – someone inside the deal has double-crossed everybody – and the shoot-out becomes even more chaotic.

There is an enormous sense of play about the film, as characters scramble from vantage point to cover and back again. Insults and jibes fly as regularly as the bullets. People get shot, people die, and yet the whole thing plays out as one of the funnier comedies I have seen in some time. Martin (Babou Ceesay), a former Black Panther and heavyweight back-up for Vernon, gets shot in the head quite early on but continues to stagger about for the rest of the film. ‘I’m not dead,’ he deliriously claims at one point, ‘I’m just regrouping.’ Other wounds are deliberately small-scale: a glancing blow of an arm here, a bullet in the leg there. It keeps the violence going on an almost non-stop basis while keeping the cast alive for perversely long lengths of time. It is impressive just how long Wheatley sustains the carnage without it ever becoming repetitive or boring.

The film benefits enormously from its 1970s setting. That is allows Wheatley to make one side the IRA is almost an irrelevance. It is the opportunities the period setting gives to the film’s costuming that makes the biggest difference. The 1970s fashion is in high and varied use throughout the picture. By contemporary standards it makes the entire cast look vaguely ridiculous, and that feeds heavily into making the overwhelming amount of gun violence as funny as it is.

Wheatley has assembled an exceptional cast for the film. It feels important, given their long partnership, to note the presence of Wheatley film stalwart Michael Smiley as senior IRA soldier Frank, but beyond that the film seems a cavalcade of strong Hollywood actors who all deserve to be more famous than they are: Sharlto Copley, Brie Larson, Cillian Murphy, Armie Hammer, Noah Taylor and Patrick Bergin all turn up to be variously shot, maimed and murdered. They work brilliantly as an ensemble, with the film keeping a fairly even hand over everybody and avoiding the use of a singular protagonist.

Ben Wheatley has enjoyed a varied career as a director, with a broad spread of genre and style represented by each of his films. Free Fire just might be the best film he has directed so far.