As a student at Bristol University in the late 1990s Laura Wade, state school-educated and from Sheffield, was not consumed by matters of class distinction. Yet on walks past the history of art faculty she did start to notice "a lot of good hair". "It was glossy hair. And that was just the boys," she has recalled. "I was in the drama department, and we were a bit more of a motley bunch."

The memory of luxuriant locks, the sheen of well-bred youth who might have looked more at home at Oxbridge, later inspired a joke in Posh, the play that made Wade famous in 2010. One of her "glossy" Oxford characters dismisses Bristol as the place where all the Dreaming Spires' rejects go.

Wade is now an accomplished 36-year-old West End playwright who has written about death, terminal illness and what might have happened to the lead female characters in Shakespeare's The Winter's Tale during their 16-year exile from court. Now she is once again defending her assumptions about the upper classes because the film version of Posh, re-titled The Riot Club, opens this month, and Wade has adapted the screenplay.

Directed by Dane Lone Scherfig, who made the equally English film An Education in 2009, Wade's story still centres on a group of overprivileged undergraduates who set about getting "chateaued" at a "trashable" dining club venue one night. The film bears the tag line "Filthy. Rich. Spoilt. Rotten", but perhaps it is the unofficial motto of Oxford's real-life Bullingdon Club, "I like the sound of breaking glass," that gives a clearer idea of the destructive decadence at its core.

Wade's play has been opened up, with scenes in a soft-top Aston Martin, and a new character added. For the theatre director Thea Sharrock this translation to screen is a big success: "I loved it even more than the play," Sharrock said this weekend. "Laura is bloody brilliant. She's full of bravery and only ever challenges herself."

Film4, which produced The Riot Club with Blueprint Pictures and the BFI, had its eyes on Wade as soon as it knew the play was under way, according to commissioning executive Sam Lavender: " It was beautifully written, witty, tough and humane, and she clearly had a great ear for the voices of these young men. I saw it a couple of times more after its transfer to the West End, and half the fun for me became watching the crowd's reactions to her characters, how torn they were between liking and judging these guys. That takes great skill to pull off."

Throughout the long development process, Lavender adds, Wade kept a close hold on the boys she had created.

Researching the original play in 2007 was tricky, Wade has said, because: "There isn't a website that helps." The daughter of a Sheffield computer programmer, she had teamed up with director Lyndsey Turner at The Royal Court theatre to develop a project about wealth and privilege among the young. By the end, Wade said she felt her background might actually have been an advantage: "It was freeing because it meant I had room to make stuff up and imagine my way behind that closed door, and try to take the audience with me," she said.

Wade did have an Oxbridge informant at close hand, however. Her boyfriend Samuel West, the actor and director who is the father of her five-month-old daughter, was an Oxford contemporary of Boris Johnson and David Cameron (former members of the Bullingdon) and so would have been able to glimpse their debauched, dinner-jacketed antics as he biked off to a student play rehearsal.

West, like Wade, has earned a radical reputation due to his outspoken comments about politics and arts funding. Their new daughter joins what some would call an acting dynasty as the grandchild of Prunella Scales and Timothy West. Samuel, however, says the Wests are a family business and not a dynasty. Whatever the West legacy, there is a tradition of political activism. Three years ago, at 76, Grandfather West demonstrated against tax avoidance, urged on by Scales.

Cinema audiences may wonder whether a new character in Wade's screenplay – a state school undergraduate from Huddersfield called Lauren Small – is intended to represent the author herself. Initially no more than love interest, her later mistreatment makes the class conflict all too tangible. Wade's first play as an A-level student also featured a character close to her own experience. Limbo was staged in a studio at the prestigious Crucible theatre and was all about "a teenage girl in Sheffield going through extremely mild emotional difficulties", Wade once recalled. "I'm very good at research," she added.

In her 20s Wade's career built quickly, with two chilling plays, Breathing Corpses and Colder Than Here, staged in 2005, and an adaptation of Alice in Wonderland in 2010. But it was Posh that caught the mood of the times, opening on the eve of a general election. Interviewed in the Observer before the first night, Wade insisted she had not painted a hackneyed portrait of the ex-Etonians who now wanted to lead Britain. "There is this cliched idea of poshness that crops up in television: Tim Nice But Dim. It's all a bit 'rah'. But as we went on, I realised it was important that the play's voices be modern,too."

Wade has now tuned up the language of the screenplay. "It's like a musical score," she says. "The script exists as a top line, and then there's an underscore of banter that needs to happen all the time to make it feel like a lively dinner with lots of conversations all around the table rather than people taking turns to speak as they do on stage."

Wade was always concerned the characters should not come across "as just irredeemable rotters". Yet even a fan of the play, the Times's Benedict Nightingale, called Posh "a paranoid throwback to the era of class warfare".

Whoever called a truce on class warfare may have to think again with the release of The Riot Club. Wade is sure the topic is a draw for an audience. "We love watching rich people behave badly. It has a sort of grisly fascination."

Wade is one of a dizzying generation of talented young women playwrights, including Lucy Prebble, Phoebe Waller-Bridge, Polly Stenham, Lucy Kirkwood, Alecky Blythe, Nina Raine and Bola Agbaje. Prebble, who wrote the hit play Enron in which West starred, is a great admirer of Wade. "Laura is a superb writer," she told the Observer this weekend. "Her works are as powerfully constructed and lustrous as diamond. Nobody of our generation has taught me more about combining formal control with spirited innovation. She has those qualities of a great writer – humility, intelligence and a rare ability to listen, and seldom seeks the limelight, preferring to turn it where it belongs, towards illuminating the stage."

Wade has talked about a fresh confidence among women writers, allowing them to tackle themes that are no "less epic or political or brutal or beautiful than the stuff male writers produce". And the zest for a fight clearly drives her, although no one ever went broke in theatre or film by presenting nice young men with glossy hair, whatever the radical sentiment. The film stars a trio of young British screen heartthrobs, Douglas Booth, Max Irons and Sam Clafin, to sweeten the pill.

Irons was initially repelled by the young characters in the screenplay, but then was seduced by Wade's purpose. "I found it unpleasant – the elitism involved." But he read again, more slowly, and discovered Wade hadn't glamorised it at all. She had "opened a window into a world that most people don't see. I thought, well, that is quite an important thing that needs to happen."