Demand for Book Five has grown even more since the film of the first book had its world premiere in London at the weekend and got rave reviews.

Millionaire author JK went back to her home in Edinburgh for a special charity screening of the film, and admitted she was busy writing.

'Very hard'

When asked when the fifth book would be out, JK said: "That's the question I get asked more than any, and I still don't know.

"It's still not finished but I am writing very hard, so it shouldn't be too long."

Secrets

JK wrote the majority of the Harry Potter books in a cafe in Edinburgh, with her then new-born daughter Jessica at her side.