When the curtain rises at the Duke of York's Theatre in St Martin's Lane, London, tonight, Polly Stenham will become the youngest playwright to make a West End debut for 42 years.

She was 19 when she wrote That Face, a corrosive portrait of a dysfunctional middle-class family, incorporating addiction, boarding school bullying and an Oedipal twist.

The Times described the play as “a fizzing, glittering firework display of fresh talent” when it opened at the Royal Court's Upstairs Studio Theatre last April. Charles Spencer, of The Daily Telegraph, saluted “one of the most astonishing debuts I have seen in more than 30 years”.

Now Stenham, 21, needs to steel herself for a backlash, according to a playwright who can understand her first-night nerves. Christopher Hampton was 18 when he wrote When Did You Last See My Mother and 20 when it moved, like Stenham's play, from the Royal Court to the commercial bearpit of the West End in 1966. Although he has gone on to achieve worldwide acclaim, winning an Olivier award and an Oscar, he has never had reviews as good again, he says.

He told The Times last night that his career was almost derailed by the response to his second play, Total Eclipse.

“There are confusing things about early success. You can drive yourself mad thinking, ‘What do I do to top that?' and I probably took 10 to 12 years to figure out that the thing is to enjoy the work, rather than worrying about how it fares.”

Hampton, along with Tom Stoppard, Harold Pinter and Nicholas Hytner, was one of the few who caught That Face on its run at the 85-seat Theatre Upstairs.

“I was very impressed. I hope someone stays with Polly Stenham and nurses her along a little bit [because] you have to be tough to cope with the ups and downs.”

So far there have only been ups. Stenham won the Critics' Circle award and the Evening Standard award for most promising playwright and has been given a UK Film Council grant to adapt That Face for the big screen.

However, with tweaking time fast running out, she is anxious about how her play will work in a much larger theatre.

“I think there has been too much hype about it,” she said. “I think it's a good play but this has been the most ridiculously amazing reaction to something that I never thought would leave my bedroom.”

Part of That Face's impact stemmed from its savage take on an unfamiliar stage milieu: middle-class Britain.

Stenham herself comes from a privileged background - the daughter of the late Unilever tycoon and art patron, Anthony “Cob” Stenham. She went to Wycombe Abbey and Rugby before dropping out of university to join the Royal Court's Young Writers programme.

Dominic Cooke, director of the Royal Court, said Stenham's play had a classical feel, reminiscent of Tennessee Williams and Edward Albee but expressed with a “punk spirit” that was all her own. “I think there are dangers to having success this young but Polly is very level headed. She just wants to focus on her skills.”

If the critics turn against her, Stenham can draw comfort from another good example. Fifty years ago this month another promising young playwright presented his debut play at the Lyric Hammersmith, where it was mauled by the critics and closed after eight days. Harold Pinter has done reasonably well since.

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