Posh, by Laura Wade, premièred at the Royal Court during the 2010 elections and depicts the fictional Riot Club, a parody of the real life Bullingdon Club, an exclusive Oxford dining society whose former members include David Cameron, Boris Johnson and George Osborne. It is about what happens when the elite club – and by inference, an elitist society – gets out of hand.

The characters are spot-on, and so is the satire. The play's first and final scenes take place between a Tory MP and his godson over a whisky in a stuffily furnished room in Westminster. In the first, an extravagant dinner is being planned and in the last the mess made by that dinner is being cleaned up – by handing over large sums of money and calling in a lawyer. For the rest of the play we, like the ten riot club members, are locked in the private dining room of a country pub in a village outside Oxford. It is this term's venue for one of their famous dinners, and post-dinner trashings. Over the course of the night there is no leaving the room (these are the rules of the club) – so the men piss out of the window and vomit into the bin bags they've brought along especially. The scenes of drunkenness are truly disgusting.

The way Wade weaves extreme Toryism in with all this is effective. Alistair Ryle (Leo Bill) holds forth on poor people with some repellent views that are uncomfortable even for some of the others round the table. But his way of talking – the mannerisms and confidence – are Cameron-ish, and it is easy to see how with a bit of coaching and a pinch of pragmatism he could rise though the party ranks. As well as offering a critique of our current leaders and the corrupt system that got them where they are, Posh is about social class is a broader sense.

When the escort that has been hired for the night refuses to crouch under the table and perform oral sex on the ten men, we meet a modern character – a warm and straight-forward Charlotte Lucus – who is completely believable. It is how realistic the rest of the characters are that really throws the Rioters into perspective. Some of the most memorable lines concern how they feel they fit in with the rest of the world: when one of them manages to make small talk at the bar by buying a drink for a couple of locals, a fellow Rioter tells him: “Dr Doolittle could talk to animals but that didn't mean the animals wanted to be his mate”. Their understanding of how they fit in can b esurprisingly lucid.

There are plenty of witty lines in Posh, along with some Oxford gags and shifty laughs of recognition from the audience. The cast also get a lot of too-easy laughs for saying things like “yah, yah”. This was a cliché of posh even by the end of the 80s and some of the actors let Laura Wade's perceptive script down by playing up to such easy public schoolboy-isms. As one of the characters himself retorts, “We're not from the 80s we're from now.” Wade's grasp of the language is impressive – when someone says “totes” someone else says “don't say 'totes', you're a parody of yourself”. The self-conscious use of chav-raa words like these mix in with the long words that were in their essay titles this week, making for some hugely entertaining dialogue.

From time to time, the ten members perform an a capella burst of a modern soundtrack. It is another disorientating reminder that these people aren't the passive remnants of a fusty old tradition, but active members of a tradition that is alive and well and continues to produce the nation's leaders. Since Posh was first staged in 2010, Wade has updated it by including references to the coalition government. Her attention to the way modernity sits alongside this kind of lifestyle is interesting. Like the escort, the landlord – beautifully acted by Steffan Rhodri – is a highly realistic character, next to whom the arguments over whether the National Trust should be able to stick ropes and posts all round your house for the tourists feel less real.

If you've read it, Posh gets a bit Zuleika Dobson at times – the oil-painted portraits move in their gilt frames and, amid bickering over future presidency of the club, the 18th century founder Lord Ryott appears as an apparition. These fantastical touches bring another dimension to the piece, adding to the orgiastic mood while showing that it can go too far; that the surreal feats of upper class hedonism sometimes get out of control.

Posh, at Duke of York'sBecky Brewis reviews Posh at the Duke of Yorks Theatre.5