YEARS AGO, I stalked Angela Carter.

Well, to be truthful, I followed her along Edinburgh's George Street during the Festival. I can still picture the tall, pink-cheeked woman, with her puff of silver-white hair that resembled a powdered wig, striding out, long skirt and baggy tweed jacket flapping. She looked like a magnificent figure from the 18th century, an Enlightenment savant reincarnated.

I followed her because I wanted to say how much her clever, carnivalesque, sexy, scary, funny books meant to me, but I was much too nervous to approach, convinced she would be formidable in the flesh.

"Oh, you should have spoken to her," says Susannah Clapp, Carter's friend and literary executor, whose slender but pitch-perfect book, A Card From Angela Carter, marks the 20th anniversary of Carter's death on February 16 in 1992. "There was nothing intimidating about Angela," adds Clapp, who first met the writer many regard as perhaps the greatest English prose writer of the late 20th century in 1979.

A former editor at Jonathan Cape and a founder of the London Review Of Books, Bath-born-and-bred Clapp asked a mutual friend, publisher Liz Calder, to introduce her to Carter because she wanted her to write for the paper. "I was thrilled when she agreed," Clapp recalls over a picnic lunch, which she has generously provided, in the offices of her Bloomsbury-based publishers.

Their friendship – personal and professional – lasted for 12 years until Carter's premature death, aged 51, from lung cancer. Carter had asked Clapp to become her literary executor. Clapp was to do whatever was necessary to "make money for my boys": her husband Mark Pearce (now married to novelist Rose Boyt, with whom he has two children) and their son Alexander, who was born when Carter was 43.

There was to be no holding back on grounds of good taste; she had no objections to her luscious, dandyfied prose – "helter-skelter hoopla" is Clapp's glorious description of Carter's gorgeous, bejewelled, tumbling style – being turned into an extravaganza on ice. "On the contrary. Her only stipulation was that Michael Winner should not get his hands on it," writes Clapp.

When she died, Carter had published 15 books, including nine novels, short stories and essays, from The Magic Toyshop and The Bloody Chamber to Nights At The Circus and her sparkling, final novel Wise Children, as well as radio, film and play scripts. The writer Paul Barker has written that she "lit up the literary scene like a gaudy firework display".

For Clapp, Carter "lit up" the London Review Of Books' pages over a dozen years, writing about everything from the ANC to Colette. "She really was an excellent journalist, with an ability to grab large subjects and turn in the most pungent pieces, although she wasn't that easy to winkle copy out of. There were, however, some delicious, long phone conversations, which I now recognise as typical of anyone who works from home and longs to be interrupted," notes Clapp. "I trod on a rabid squirrel," was the excuse for one missed deadline.

Over the years Carter – the daughter of a Fleet Street journalist, Hugh Stalker, from Aberdeenshire, and a polite South Londoner mother, who had been a cashier at Selfridges – sent Clapp, now a renowned theatre critic and broadcaster, a trail of surreal, ribald, ironic postcards. Looking back on these cards – the 20th century equivalent of email – when she was writing a series of programmes for Radio 3 on postcards, Clapp had the inspired idea that they would form the basis of an informal autobiography of Carter. They would create "a paper trail, a zigzag path through the 80s," and tell of Carter's hidden histories, for the caustic message on one side often contradicted the exuberant image on the card or vice versa.

"Sometimes the card itself is its own message. Some tell more than one story. I had always wanted to write something about Angela anyway and this little book – just over 100 pages – sprang out of a much larger one I was commissioned to write and have yet to deliver on postcards. I had a lot of things I wanted to say about Angela, but not really a memoir as such; I had always resisted that. For me it's easier to write obliquely rather than full on," says Clapp, who wrote a marvellous, miniature memoir of another friend, the late writer Bruce Chatwin, With Chatwin (1997).

"I didn't always want to go around writing about my dead friends," Clapp confesses. "It didn't seem very good luck for my existing friends apart from anything else, also it seemed rather peculiar."

The Carter estate has now appointed an official biographer, Edmund Gordon, who will publish in five or six years. "I am pleased to have found a young man who is so passionately interested in her work. I like to think he will alert a new generation to her, because she is, I think, over-identified with a feminist constituency, which of course she was, but there was more to her.

"When I asked her which came first, feminism or socialism, she didn't have any doubt – socialism was the most important thing and it was one of the things I most admired about her, not simply that our politics overlapped, which they did, but the fact she was so fiercely forthright about them. We miss her incendiary ideas and her voice in so many ways. I would have loved to read her – not on the present shower, but on Blair, his plausiblity and his duplicity," adds Clapp.

Carter, she says, was austere, she was voluptuous; she was domestic, she was exotic; she was hesitant, she was fluent; she was polite, she was ferocious; she was kind, she was caustic; she was innocent, she was quizzical. "She had a gentleness, which overlay a steeliness," Clapp explains, adding that Carter also took great pride in her father's Scottish background. "That was a big thing with her, although there was an ambivalence about her relationship with her parents, but she always had a close attachment to her father. She was very drawn to northern cultures and Scottish fairytales. She felt it was something to do with her central being."

The endpapers of A Card From Angela Carter reproduce the artist Corinna Sargood's drawing for the invitation sent out to Carter's memorial gathering in Brixton's Ritzy cinema. It was to Sargood, one of her oldest friends with whom she shared an eccentric mania for collecting sardine tins, that Carter remarked on the phone, soon after the news of her illness had broken, "Oh, a man's coming to the door." Pause. "It's all right. I'll let him in. He hasn't got a scythe." Sargood's drawing is celebratory, showing a menagerie of on-stage animals and a champagne glass.

Clapp's book – serialised on Radio 4 this week – leads the celebrations, ranging from a Bloomsbury salon on Thursday to a Royal Society Of Literature event. Carter's admirers, such as the Scottish novelist Ali Smith, who constantly re-reads Carter, are championing her life and work. "I read the glorious Wise Children on publication," says Smith. "I couldn't believe the energy, the generosity of it. So I went back and read everything she had written in chronological order, then I read Wise Children again and I saw where the glorious, open, richness in her work came from. She's great. Totally uncompromising."

Meanwhile, some of Carter's poems – "which are very, very pungent... that word again!" declares Clapp – are being set to music, under the auspices of pianist Joanna MacGregor, and will be broadcast on radio later this year. "It was the writer and academic Marina Warner's idea," explains Clapp. "She's so enthusiastic about them and I have a couple in the book. They share many of the themes of Angela's books, of course, the fairytale and feminist aspects and her interest in medieval literature."

Warner, who has just judged a competition for an illustrator for a new Folio edition of The Bloody Chamber, is also enthusiastic about Clapp's book, which she thinks "perfect". She believes Carter's work has never dated. "If anything it has become more vivid, especially among young women for whom she might as well be as distant as Virginia Woolf, but because she writes with such ferocity about curiosity and sexual desire, she speaks to them with immediacy, also to young men. It's the gorgeous fabric of her imagination that is so marvellous. She's the Fairy Godmother of English Literature."

Everyone who knew Carter speaks of her extraordinary, witchy appearance. "I first met her in the late 1960s when she published a story that became The Bloody Chamber in Vogue, where I was working," Warner recalls. "She was very thin, with light red hair and a red beret. She already had this ironic twist to her mouth, always looking as if she were suppressing a bubble of laughter."

A Card From Angela Carter by Susannah Clapp is published by Bloomsbury, £10. Writing In Three Dimensions, a programme on Angela Carter's radio plays, is on Radio 4, Thursday, 11.30am. Bidisha chairs a discussion about Angela Carter, with Susannah Clapp and Marina Warner, at Aye Write!, in Glasgow on March 17; for tickets call 0141 353 8000 or visit www.ayewrite.com