"It's like Beatlemania," muttered a baffled-looking policeman surveying the crowds outside the Royal Albert Hall yesterday.

There were plenty of excited screams, but some notable differences. For one, the average age of the fans was closer to seven than 17, and for another, instead of brandishing posters from magazines or record sleeves, the fans were all waving books above their heads - Harry Potter books, to be precise. Yester day, for one brief afternoon, JK Rowling was playing at the Albert Hall.

And while it wasn't quite Beatlemania it was, as the author told screaming audience members as she took to the stage, as close as she was likely to get.

Indeed, the whole event was like a rock concert, albeit with a touch of the panto. There were warm-up acts, audience chants, even onstage pyrotechnics. A far cry from Rowling's first book reading which, she later recounted, had an audience of two people.

But this is not your average book reading. As Stephen Fry, who was playing the Q role in the Q&A part of the event, boomed: "We are here to meet the most famous and the most popular writer in the whole wide world!" And out she stepped, seeming somewhat dazed as she looked out at the shrieking crowd of 4,000, plus web cameras, perhaps marvelling at where an idea she famously conceived on a train journey from Manchester had brought her.

After settling some vital points - it's "Rowling, as in rolling pin" - it was down to the important stuff. If she was a teacher at Hogwarts she would teach charms; she got the idea for quidditch after an argument with her "then boyfriend, [I] walked out of the house, and sat down and invent[ed] Quidditch. Maybe in my darkest soul I'd like to see him hit by a bludger." And, no, she doesn't believe in magic - cue collective gasp. Asked if she would ever write about Harry after Hogwarts, the smiling answer was we "have to wait and see if he survives to be a grown-up". Cue a sharper gasp. When Rowling read from the novel, the audience looked as enthralled as pop fans at the opening of a favourite song. But not as pleased, perhaps, as the Bloomsbury publishing folk, were as happy as Harry.