A SINGLE mother of 34 and a bespectacled orphan schoolboy may not be the most promising combination, but together they have become the publishing sensation of the past two years.

The latest chapter in the remarkable story of Joanna Rowling's beguiling literary creation began yesterday with the paperback publication of the second book in her Harry Potter series, Harry Potter and the Chamber of Secrets.

Potter is the schoolboy wizard whose enthusiastic adoption by children and grown-ups in their hundreds of thousands has had critics hailing Ms Rowling as the new Roald Dahl.

Platform One at King's Cross Station briefly becomes the mythical Platform 9 and three-quarters, the place from which young Harry departs for school at the beginning of each new term and which functions like the wardrobe in C S Lewis's Narnia chronicles.

Harry Potter and the Philosopher's Stone, the first in what will eventually develop into a seven-part series, introduced the eponymous hero to a generation of computer games junkies previously thought to have been lost to the charms of print. The results have been extraordinary. Sales of the two books are now nudging half-a-million, while the hardback version of Chamber of Secrets spent its first month on the shelf as the bestseller across all books.

Ms Rowling has garnered an armful of awards, including the Smarties Book Prize (the children's equivalent of the Booker) in consecutive years and a place on the 1998 Whitbread shortlist. Hollywood lent its validation last autumn when Warner Brothers secured the film rights to both books for a seven-figure sum.

Master Potter is an orphan forced to live under the stairs by cruel relatives until he learns on his 11th birthday that he is, in fact, the son of famous wizards, whereupon he is whisked off to Hogwart's School of Witchcraft and Wizardry. There he takes lessons in potions, herb lore and Quidditch, a kind of football played on broomsticks. Oh yes, and he saves the school and the world from the fallen angel Lord Voldemort, a former head boy of Hogwarts, who chooses to turn his magic against the institution. In other words, a ripping yarn of good versus evil that legitimately conjures up the New Testament, only with characters that recall Roald Dahl.

The names of Dahl and C S Lewis are frequently mentioned alongside Ms Rowling's, a comparison at which she has balks. "C S Lewis is quite simply a genius and I'm not a genius," she said. "And while I think Dahl is a master at what he did, I do think my books are more moral than his. He also wrote very overblown comic characters, whereas I think mine are more three-dimensional."

Either way, critics have universally lauded Ms Rowling's as she carries readers into a world of invention where Harry flies a car into a tree in flagrant breach of rules on the misuse of Muggle (as normal people are known) artefacts. In the second book Harry unravels the secrets of giant spiders, schoolmates turned to stone and an unpleasant creature that has taken to lurking in the school plumbing.

Potter was drawn with spectacles because, Ms Rowling said, she had worn thick glasses as a child and was frustrated that "speccies" were swots but never heroes.

Nominally pitched at 9 to 12-year-olds, Harry's appeal has been broader. Parents who were complaining about their children's refusal to turn off the light until they had finished one more chapter became the next Potter converts. The publishers Bloomsbury took the unusual step of bringing out an adult version of the first book last September. It was wrapped in a design-conscious cover featuring a black and white photograph of a steam train with the title flashed in citrus orange letter. The idea was to spare adult readers on public transport the chore of hiding the children's version behind their morning paper.

If Harry's adventures make for compelling reading, then Ms Rowling's story is also worth a chapter or two. After working for Amnesty International, she went to Portugal to teach English. There she married a journalist, but within weeks of the birth of a daughter, Jessica, they had separated.

Divorced, penniless and now a single mother, she returned to Edinburgh, where her sister lived. Much of the first novel was written in Nicolson's, a cafe in the city where she would escape her cold and miserable flat. While Jessica slept in her pram, Ms Rowling stretched out her coffees and scribbled furiously away in long hand.

The manuscript was dispatched to Penguin, who turned it down, and then HarperCollins, where it gathered dust for a year. Finally she enlisted the help of a literary agent and, within a day of sending the book, Bloomsbury gratefully snaffled it up. The rest could well be literary and cinematic history.