The Jane Austen-hits-LA comedy changed fashion, language and cinema. As it turns 30 and a new stage musical version opens, its writer and director discusses why it's so personal to her.

Back in 1995, Clueless offered a cheeky update of Jane Austen's Emma in a Los Angeles high school and, without even seeming to try, revolutionised how we dress and talk. Tartan and preppy chic are still huge (note the blazer and mini-skirt wore by Taylor Swift in London last August, or the pop star's yellow-and-black combo at an MTV awards do in September). Meanwhile, "As if!", the catchphrase of its heroine Cher, which originated as a piece of Californian slang, has become ubiquitous. Will you be spared the phrase in this article? As if!

Because the film is brightly coloured and revolves around teenage girls, some critics at the time undersold the sharpness of its satire, which targets (among other things) white, west coast privilege, the plastic surgery industry, celebrity do-gooding, taboos surrounding menstruation, the cruelly low wages of teachers, and the kind of Nietzsche-reading liberal male who feels compelled to grow a goatee.

The popularity of Clueless triggered a rash of insouciantly smart high-school-meets-classic literature movies (including 10 Things I Hate About You, Cruel Intentions, and Easy A, to name but a few). Just as importantly, it started a trend for films and TV shows that focussed on friendships between teenage girls. Thanks not only to the script but also a flawless cast and tip-top soundtrack (so much Radiohead), audiences of all ages found themselves rooting for salty protagonists, Cher, Dionne and Tai, who dominate the proceedings in a way that hadn't been seen before in a mainstream US film. Yes, there's a rom-com element to the plot, but it's the tensions between the girls that generate the most heat. Cher's complex interactions with Dionne and Tai paved the way for Buffy and Willow's textured relationship in the TV series Buffy the Vampire Slayer. Also, not to be bitchy, but without Clueless there'd be no Mean Girls. And Olivia Wilde cited it as an inspiration for her riotous directing debut, Booksmart, itself a modern teen movie classic.

Yet 70 year-old Amy Heckerling, the film's writer-director, claims she had no idea Clueless would be a hit. "Nobody is ever sure of that," she tells the BBC. "Well, maybe some people are sure of it. Not me." Nor does she know if a new West End musical based on the film, for which she wrote the book, will click with audiences; it is currently running in previews ahead of an opening night in March. What matters, she says, is that she enjoyed working on both projects. She says of the musical, "It will either work or it won't, but I'm loving doing it." As for the film, "I have to admit, on that shoot I was happier than I've ever been. There were no big prima donnas. It was the closest I've ever come to imagining a movie in my brain and seeing it unfold exactly how I imagined."

In the last three decades there's also been a three-season Clueless TV show, a book series, and another go at a stage musical, which premiered on Broadway in 2018. Still, it's the original film we keep coming back to and that Heckerling, Zooming from her home in New York, wants to discuss.

As in Austen's 1815 novel, the plot revolves around a self-absorbed daddy's girl. Cher (Alicia Silverstone; putty-soft and irresistible) bombs around Beverly Hills with best-friend Dionne (Stacey Dash; poised), obsessed with matchmaking and make-overs. Cher is determined to "help" a new girl at school – dishevelled New Yorker Tai (Brittany Murphy; volcanically beguiling) – and proceeds to treat Tai like a toy. That is, until Tai fights back and Cher, her mind blown, realises that Tai is her equal. Which is where Heckerling veers off from Austen (whose heroine is ultimately horrified by her protege's "notions of self-consequence"). Here's the truth about Clueless. It's not as good as Emma. It's way better.

Heckerling suspects that the film has such a loyal following (and keeps picking up new acolytes) because its "two princesses",........

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