Timberlake Wertenbaker is not a happy woman. The great playwright talks to Michael Billington

Just imagine. If Timberlake Wertenbaker wrote a new play for the National with a cast headed by Harriet Walter, Olympia Dukakis, Alan Howard and Joseph Fiennes, she'd get headline reviews. But because her latest work, Dianeira, goes out on Sunday on Radio 3 with just such a cast, it will presumably get the random coverage we reserve for a marginalised medium. Radio is 10 times more vibrant than television; yet, within the cultural hierarchy, it remains a poor relation.

What is fascinating about Dianeira is that it brings together many of Wertenbaker's constant themes. A critique of male values; a fascination with storytelling; above all, an obsession with classical myths. In this case, she has seized on the story - also told by Sophocles in his virtually unknown Women of Trachis - of Herakles's abused wife. Dianeira suffers the absence of her heroic husband. She also has to endure the presence of his captive young mistress, Iole. And when she tries to recapture his love with the help of a magic charm, she brings about a heap of destruction.

Anger is the story's theme; and I discover, not for the first time, there's a good deal of anger bubbling away inside the soft-spoken, stylish Wertenbaker. A few years ago we locked horns, at a Texan university celebration of post-war British drama, on the subject of laddish new writing. And, as I interrupt her afternoon piano practice in her sunlit north London home, I find she still has strong views on women's inferior theatrical status. But first I'm intrigued to know why she has this big thing about the Greeks.

"Funny you ask that," she says. "When Catherine Bailey commissioned me to write a radio play and I floated the idea of a Sophoclean translation, she said, 'Don't do me a boring Greek or no one will listen.' So what I've tried to do is review an ancient myth from a totally modern standpoint. The play's really about the way anger threads its way through the generations on both a personal and political level. I've also tried to draw parallels with the Balkans today, where the cycle of revenge continues and where neighbour is still fighting neighbour.

"But I suppose I'm drawn to the Greeks by love and passion. I studied for a time at the French Lycée in New York and came across this book full of marvellous pictures of boats which turned out to be The Odyssey. I also did Greek at university and later hitchhiked around the country. But what I love about the Greeks is that they're trying to define what a human being is about. There's a combination of tremendous despair, which runs through Sophocles, and great hope - a terrifying bleakness and, at the same time, a love for the individual. They're also suspicious of the state and have a sense that life is out of control, something I certainly understand as a writer. But all those things are back in question again after the 19th century, which believed it had all the grand solutions."

Wertenbaker's own career has also had fluctuations of fortune. She was a beacon of hope in the theatrically drab, Thatcherite 80s, making her mark with a succession of brilliant Royal Court plays: The Grace of Mary Traverse, Our Country's Good and, at the start of a new decade, Three Birds Alighting on a Field. She received a lot of critical flak, however, in 1995 for The Break of Day - conceived as a companion piece for Three Sisters - only to recover form last year with the fascinating After Darwin.

What seemed to throw her was the departure of her trusted director, Max Stafford-Clark, from the Royal Court, and the sudden bullish emphasis on plays about the male ego. Given her insecurity, does she feel a writer needs a home?

"Absolutely. I now feel completely homeless. I am currently writing a play for the Court, and Ian Rickson has been very good about keeping in touch, but I don't have the sense of a guaranteed production that I did under Max. I also resigned from the Royal Court board because I was deeply unhappy. It was partly because of the increasing encroachment of private sponsorship, which I passionately believe is dangerous for new writing - partly because of seemingly trivial things like the new leather seats. Every time I took up a cause, it was lost; and I began to feel like Don Quixote, still talking about the age of chivalry. I don't want to open up a lot of old wounds, but as the only playwright on the board, after Winsome Pinnock left, I began to feel anachronistic."

Wertenbaker also found herself out of sympathy in the mid-90s with the sudden rush of plays by male dramatists. "There was," she says, "a particular moment when there were all these plays by men about men with really no women present. You go to the theatre partly to be mirrored in some way and you begin to feel you don't exist. I don't think women have ever been a welcome voice. You sense a relief that we can shut those women up and get back to what really matters, which is what men are saying. It's not complete paranoia. I think we're trained from birth to listen to men. The disappearance of women from the stage may also have discouraged aspiring writers. Word got around that there was little point in sending your play to the Court or the National. So women just stopped. Or went into TV and films."

But isn't Wertenbaker treating an accidental phenomenon - the sudden emergence of Marber, Ravenhill, Butterworth, Penhall et al - as a permanent condition? And weren't the best writers critical of male values? Can one also fairly attack the Court for neglecting women when it was presenting plays by Sarah Kane, Phyllis Nagy and Rebecca Prichard?

"Sarah Kane," admits Wertenbaker, "did generate imitators, but I think she was incorporated into the male group of the period. She was seen as one of the boys. But if you see a dominance of male dramatists going on for a long period of time, when women are equally educated, equally able to write, equally bold on stage, you have to ask yourself why.

"We talk about women dramatists, but it's significant that 'woman' becomes the compound whereas 'male' is the noun. It's as if that's the norm. I don't even think the prejudice is conscious. It's just that men judge the plays, put on the plays and, on the whole, run the theatres."

Point taken. But Wertenbaker has created a formidable body of work, and it's significant that in Dianeira she not only appears as a narrator recounting the memories of a cafe storyteller (Dukakis) but also co-directs with Catherine Bailey.

She still claims to feel, partly because of her mixed American-French background and partly because she is a woman, something of an outsider in the British theatrical establishment: a tolerated guest rather than a permanent resident. But I suspect the very qualities that make her an outsider are also the ones that have made her a good writer: an ability to view British life from a critical distance and to explore the contemporary meaning of classical myths. And in Dianeira she looks back on anger with a passionate political concern.