As the closest UK General Election in recent history looms large and everyone talks about the economy and inequality, that defining moment of the noughties – the Iraq War – feels almost forgotten. Most politicians are probably very happy about that. But if any film is capable of reminding you of the incompetence and political trickery of the time, it’s In the Loop. Written and directed by British comedy heavyweight Armando Iannucci (with further writing from Simon Blackwell, Tony Roche, Jesse Armstrong and Ian Martin), it’s a piercingly satirical look at the UK’s decision to launch the Iraq War alongside the USA, and despite everything that’s changed in the political landscape since, it’s as potent and hilarious as ever.

Created by the team behind classic sitcom The Thick of It and featuring many of the same characters, In the Loop begins with a simple slip-up that defines so much of the political doublespeak and comedy within the film. Minister of International Development, Simon Foster (Tom Hollander) is speaking about the “war on preventable diseases” in an interview when he is suddenly challenged about the likelihood of a war in the Middle East. In his personal opinion it is “unforeseeable”. Enter the dragon: Malcolm Tucker.

Played to snarling, throaty perfection by Peter Capaldi, Tucker is the government’s spin doctor of doom, managing “communications” to the outside world with brutal ferocity and no hint of morals. His response to Simon’s interview is that “He did not say “unforeseeable”. You may have heard him say that, but he did not say that. And that is a fact.” In this world, nothing is true or certain until it’s already happened, and even that’s no guarantee. The Government’s aim is to hover in a state of diplomatic indecision, neither committing to nor ruling out a war until suddenly, behind closed doors, a decision has been made.

It’s the perfect situation for Tucker, as when war is, in his own words, “neither foreseeable nor unforeseeable,” it makes dissent that much harder. You can’t protest against something that is still just a vague possibility, and the moment it becomes anything more concrete than that, it’s too late.

Staggering from incompetence to pure idiocy, Simon tries to bullshit his way out of the hole he’s dug by announcing that “sometimes, to walk the road of peace, you must climb the mountain of conflict,” just like, as Malcolm puts it, “a Nazi Julie Andrews.” As well as excelling at skewering the dark arts of politics, In the Loop has a fine sideline in eloquent swearing, using well-placed “fucks” to lethal effect.

The farce is also strong with this film, with the seriousness of the political situation contrasted with the bizarre scenarios in which the cast find themselves. From working out the number of available troops on a child’s toy computer to bringing forward (then delaying) a crucial UN vote, or editing crucial evidence by manipulating a lackey’s fingers for him, In the Loop is a fine example of how everybody, even those with the greatest power and responsibility, are just winging it.

The cast are mainly established in TV rather than film, but all rise brilliantly to the challenge of delivering a feature-length performance. David Rasche, Peter Capaldi and Chris Addison are all superb, but the real standout performance comes from Tom Hollander in what amounts to the lead role in this ensemble cast. He has a beautifully world-weary line delivery that turns even little throwaway comments into zingers and squeezes every possible laugh out of the already brilliant Oscar-nominated script.

Most of all though, he is a powerfully sympathetic presence amongst this cabal of cut-throat career politicians. He’s not as idealistic as some of them; really he’s just a fairly unopinionated man who somehow finds himself standing between the Western world’s governments and all-out war, but if anything that just makes him easier to root for. He may deliver his fair share of withering, sweary takedowns, but they’re normally fully deserved, like when he bollocks Toby (Chris Addison) for turning up late to a crucial meeting smelling like “a pissed seaside donkey.”

The finale is as tense as any thriller but still packed with more laughs than most sitcoms manage in a whole series. As Malcolm’s attack dog Jamie (“the crossest man in Scotland”) bullies a Foreign Office staff member to fake a report supporting the war, Simon threatens to resign in protest and Malcolm finds that, for once, he’s not the one calling the shots.

This is the real secret of In the Loop’s brilliance. It’s not just a multi-layered gagfest, but a potent political drama scrutinising the Machiavellian manoeuvring of all governments. It’s almost dystopian in its portrayal of a world where the truth is little more than a convenient piece of evidence, changeable with the tap of a keyboard. As long as it looks like the truth and helps any given politician get their way, then that’s good enough. As Assistant Secretary of State Linton Barwick puts it: “Now you may not believe that, and I may not believe that, but my God it’s a useful hypocrisy.”