In our Book Festival coverage, Anne Johnstone finds J K Rowling has changed in body, but not in mind

WHEN Harry Potter wants to float around undetected, he dons an invisibility cloak. If his creator, J K Rowling had possessed such a garment this summer she would have been wearing it a lot.

At the Edinburgh Book Festival yesterday it turned out she had settled for the next best thing - out have gone the trademark long red hair and pallid face, in have come a brown-blonde bob and a lightly sunkissed look, bequest of a recent foreign holiday.

Rowling enjoys talking to small groups of children but is clearly intimidated by big crowds. She began unsteadily, reading quietly from Harry Potter and the Prisoner of Azkaban, lending the insubstantial professor Trelawney a passable Welsh accent.

Then she went straight to questions, suddenly reasserting her old self (teacher) as she pointed to each child selected. "The boy in the middle with Weasley hair, then the girl at the back of the room with a yellow shirt and bunches."

There were few hints about the fourth Potter book currently under construction. She wouldn't reveal the title but managed to let slip that we meet Ron Weasley's two eldest brothers and witness the Quidditch World Cup, a sort of three-dimensional polo-cum-rugby played on broomsticks. "It's Ireland v Bulgaria. I won't tell you who Scotland go down to! There's a bit of crowd trouble," she hints. Also the dreadful Dudley is finally put on a diet.

The writing is getting easier "because I've built up a cast of characters".

She gallantly squares up to a question about Raymond Briggs, one of the few respected names in children's literature to dismiss her books. " I would be unbelievably arrogant if I expected the whole world to love my books. I only wish I'd been criticised by someone whose books I hated."

Rowling's compulsion to write is overwhelming. "If I could go straight out of here and write I would, but I can't. There you are, life's cruel."

A "good day" means about nine hours of solid scribbling. "I get on a high if I've written all day in a cafe. I'm really dangerous. I bounce out on to the pavement full of caffeine and buy lots of things I don't need." The fourth book is not doing so fast as she'd hoped. It's not because of the writer's block which afflicted her two years ago after the publication of Harry Potter and the Philosopher's Stone, so much as the age-old dilemma for successful authors - the more successful you are, the greater the pressure to promote and the harder it is to find writing time.

During the publication of her third book, Harry Potter and the Prisoner of Azkaban, last month, her refusal to give interviews seems further to stoke the public hysteria already surrounding the event. One paper put a bounty on her, instructing its drones to "dig the dirt" on her. Even her father was doorstepped.

EXPLAINS Rowling: "I wasn't hiding. I just needed to work" - and, in so saying, sounds uncannily like Hermione, the endearing swat and main female character in the Potter books. Unsurprisingly, Hermione is a cypher for Rowling herself as a young teenager. "Like her, I think I was really annoying, though I wasn't so clever.

"Bloomsbury has been wonderful. It really protected me. In the States it's a bit different. The books are going well but sales could be increased a lot by more promotion."

She has agreed to a three-week tour next month. Scholastic, her American publisher, has hired a posse of security guards to protect her from armies of adoring fans.

Oh, for Harry's Firebolt to rise above it all. This earth-bound high-flyer would even settle for a Nimbus 2000.