As the years rolled on, it became evident that while the bare bones of the plot might have been in Rowling's mind, there was much spadework still to be done, and Ginny's magicality eventually became buried under the role of boring love-interest. All the same, I swore to keep these details secret. 

I assumed I would easily be able to sell a feature based on the interview, even without breaking confidence. So did Rowling. We were both wrong. "Sorry, we've had enough about J.K. Rowling lately," said The Times. The Daily Mail followed suit. I shelved the idea and thanked fate, and Jessica, that I hadn't splashed out on a restaurant meal. 

Until Hollywood stepped in, the adult publishing world thought Rowling was just a surprisingly successful children's author. The book received minimal publicity help. But Harry Potter's popularity spread around playgrounds, at bus stops and up and down school dinner queues. Children loved to dive into this consummately British fantasy — the complete parallel world, the ebullient innocence, the boarding-school set-up tweaked for our time. The ablest readers instantly took it up, followed by the average readers, and then, most wonderfully of all, by the reluctant readers, who found themselves caught up in the tide. My son Tycho, then aged eight, devoured the book in days. On finishing it, he put his head in his hands and lamented, "I so wish I knew other people who had read this book, then I could talk about it with someone." 

A few years later the TV news showed us overweight American children queuing at midnight for the latest title; a few more years and the cult, along with the lives of a team of child stars, was engulfed by a movie franchise. If Tycho wants, he can now talk about Harry Potter with the world; the trouble is that when something is so well-known, its magic is lost.