Piper is 23. She has never written a book before. Yet the actress is said to have been paid more than £600,000 to write her life story, a literary Tardis that will transport readers from her birth in Swindon, through her marriage to the DJ Chris Evans, all the way to the celebrity galaxy that she now inhabits.

Piper’s memoirs are only the latest evidence of a phenomenon sweeping the publishing industry: books written by people who don’t normally write books, bought by people who don’t normally read books, being sold in places, such as supermarkets, that did not, until quite recently, sell books.

The figures are astonishing. Of the top 50 bestselling titles last year in the biography and autobiography category, half were by or about celebrities (broadly defined as anyone whose fame is TV-based). Sharon Osbourne’s book Extreme has become the bestselling hardback autobiography since records began, with more than 600,000 copies sold, followed by David Beckham’s My Side, with more than half a million sales. Sales of celebrity books are growing at an estimated 15 per cent a year.

Last year Victoria Beckham admitted: “I haven’t read a book in my life.” She has, however, written one, entitled Learning to Fly, and is now writing a children’s book. She probably won’t read that either.

Celebrity autobiographers are getting younger. Indeed, Piper is rather elderly to be penning the first instalment of her memoirs. The footballer Wayne Rooney, 20, is being paid a reported £5 million for the story of his short life, to be ghost-written by the veteran author Hunter Davies.

The singer Charlotte Church was 15 when her first autobiography, My Life (So Far), was published. At 19, she is working on a sequel, perhaps to be called My Life (A Bit Further). Brooklyn Beckham published his “diaries” at the age of 2½.

Celebrity fiction is also booming. A novel is the must-have item for every serious celebrity. Pamela Anderson, Naomi Campbell, Kirk Douglas, Joan Collins, Dolly Parton and Martina Navratilova have all written fiction. Marlon Brando recently published his first novel even though he was, in fact, dead.

Publishers and booksellers are divided over whether the torrent of books by the likes of Doctor Who’s bubbly assistant represents an alien invasion that will destroy publishing for ever, or a force for good. For every publisher lamenting that the EastEnders actress Daniella Westbrook’s book about her cocaine-crumbled nose sells more copies than the Booker Prize-winner, there is another pointing out that Piper and others are helping to uncover brave new worlds of book readers.

Some “celebiogs” are quite breathtakingly awful, mere narcissistic blotting paper, but others are genuinely revealing works of literature, offering fascinating (and occasionally inadvertent) insights into an individual’s past and personality. Lance Armstrong’s tale of cycling and cancer, It’s Not About the Bike, is not only a good memoir but also a remarkable story. A good ghostwriter (and there are many) can catch the voice of a celebrity exactly.

As one British literary agent puts it: “The celebrity memoir is the jackpot. Everyone is looking for the right combination, and by Christmas there will be half a dozen television celebrities slugging it out at the top of the bestseller lists.”

The stand-out classic of the genre is Being Jordan, the autobiography of Katie Price, glamour model, reality television contestant and miracle of cosmetic surgery. When not dwelling on the physical attributes and inadequacies of her former boyfriends, Price sings a hymn of praise to her own breasts. Indeed, the book is a perfect reflection of those breasts: artificial, overinflated and fantastically popular.

Being Jordan was turned down by successive publishers until the manuscript was bought by John Blake, of John Blake Publishing, for a meagre £10,000. The book was panned by critics, who pointed out that the author did not appear to have read her own memoirs. (“I don’t know if they’ve mentioned it in the book, but . . .” she told one interviewer, with delightful candour.)

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