Harry, who might well have outsold Furbies this Christmas, has cast his spell over a generation. The books’ realm of wizardry that co-exists with the world of humans (Muggles, as Rowling calls us) is acquiring the cult status of Terry Pratchett’s Discworld.

Even moody teenagers are willing to be seen with Harry Potter and the Philosopher’s Stone, soon to be a film. The rejacketed edition of the first Harry Potter book is considered trendy enough to be sold in Virgin stores. And like the first title, the second book, Harry Potter and the Chamber of Secrets, has won a gold award in the Smarties Prize (in which children vote for the winners). Chamber of Secrets is among the hot tips for the Whitbread Children’s Book of the Year award next month.

Since autumn 1997, when Philosopher’s Stone won the Smarties and then secured a lucrative American rights deal, its previously unknown author has been in a rare position for a children’s writer - she has become a celebrity outside the children’s book world without having to celebrate her centenary first. There is now little that is not known about 33-year-old Joanne Rowling (except that her last name rhymes with “bowling”, not “howling”).

The first flurry of media interest came after the early success of her first novel (she had spent five years writing, and showed it to nobody before sending it on spec to literary agent Christopher Little). A series of “rags-to-riches” profiles appeared, all obsessed with her single-parent status and her habit of scribbling in Edinburgh cafes while her daughter Jessica slept in a pushchair(one interviewer was disappointed when Rowling was unable to confirm that the first outline of Philosopher’s Stone had been composed on the back of a napkin). Now Jessica is at school and her mother has beenwriting full-time for more than a year.

The celebrity machine grinds on but the focus has shifted to the books and their child appeal. Harry, the have-a-go orphan hero of Hogwarts School of Wizardry and Witchcraft, has a fan club with more than 2,000 members.

His creator enjoyed her brief teaching career - three years teaching English language in Portugal followed by a stint doing supply in Edinburgh and teaching French part-time at Leith Academy - and now obviously relishes her public encounters with children. She caused a sedate gathering at the Edinburgh Book Festival to burst into spontaneous applause and recently captivated a class of sophisticated 15-year-old girls in Putney with her mock-croc platform shoes.

“My heels are a legacy of teaching,” she says. “I am only 5ft 4in tall and I was determined not to have to look up at pupils. You will never see me in flat shoes.

“Teaching was definitely something I chose rather than drifted into. I had wonderful colleagues at Leith Academy and my ideal had been to teach part-time and write part-time, but the chance to make a living from writing had to be taken.”

She remembers with affection Moray House training college in Edinburgh, where she did her PGCE and furtively typed out the manuscript of Philosopher’s Stone in the computer room. “I knew it would be considered too long for a children’s book, so I did it single-spaced to make it look shorter - and then had to do it again.”

One publishing myth - that a 10-year-old’s attention span will not stretch to 200 pages - has been demolished by the Harry Potter books. Rowling’s readers are desperate for more, so between books she raids her boxes of notebooks for spare material to publish in the fan club newspaper.

“I love visiting schools now - for a former teacher it is complete irresponsibility to whip a class into a frenzy and then leave.

“And the work generated by the books is so imaginative.” Chamber of Secrets, in particular, has led teachers to explore the way prejudice works through examination of attitudes to “mudbloods” - those of mixed wizard and Muggle ancestry (like Harry, whose mother was a Muggle). A stern moral code is applied at Hogwarts and good hastriumphed so far.

On one level these are souped-up school stories, complete with eccentric teachers, bullies and secret passages to be explored by boys left behind in the Christmas holidays. Harry studies potions, charms and transfiguration and becomes a whiz at the school sport, quidditch (basketball on broomsticks). Unlike most boarding schools, though, Hogwarts has a basilisk in the basement and the evil forces that killed Harry’s parents are ever-present.

Book two is a tighter, more complex read than book one, with fewer of the stray storylines that irritated some adult readers (but not children, who seem to appreciate the books for being the kind of sprawling stories they like to write themselves, with unwieldy plots, cliffhangers, sharp asides and in-jokes).

The author says: “I’m prouder of book two in a way because I wrote it under a lot more pressure than book one and found it much more difficult. Until book one was so successful, I was quite happy in my own private world. Nobody had read a word about Harry for five years, and suddenly there was a lot of attention. Of course I always hoped it would be read, but I had not imagined the level of personal attention I would get.”

Chamber of Secrets throws light on Rowling’s grand scheme - seven books, each covering a school year. Book three, Harry Potter and the Prisoner of Azkaban, is now with the editor at Bloomsbury Children’s Books. Book four is in progress, which means the Harry saga is already half over for its author. She spends a lot of time fielding questions - what happens when Harry hits puberty? Who’s going to die in book four? Her all-purpose reply is “trust me on this”. But she admits “number four will be a pivotal book”.

Potter power is such that Railtrack has agreed to renumber a platform at King’s Cross station to celebrate the paperback launch of Chamber of Secrets next month. (For the uninitiated, Hogwarts pupils travel on the Hogwarts Express, which leaves from platform 934 at King’s Cross. This is inaccessible to Muggle commuters - if you have to ask where it is, it’s best not to know.) “I have always visualised Hogwarts in Scotland, so it makes sense,” says Rowling. “Also, my parents met on a train from King’s Cross and it’s the most magical station in London.”

Remember, Muggles, magic is all around us.

Contact the Harry Potter Fan Club co Bloomsbury Children’s Books, 37 Soho Square, London Wl