In a private publishing venture, the Harry Potter author announced that she is to produce only seven copies of her next 160-page book The Tales of Beedle the Bard, a Harry Potter spin-off of five short fairy tales.

Rowling has decided to give six copies, each the size of a paperback, to friends who helped or supported her through the 17 years that it took her to complete the Harry Potter marathon.

She will sell the seventh at an auction by Sotheby's on December 13 to raise money for the Children's Voice, which she founded two years ago with the Euro-MP Baroness Nicholson, to campaign for the rights of European children, particularly in eastern Europe where more than one million young people are trapped in institutions in grim conditions.

Each copy, written on handmade Italian paper, is bound in leather and decorated with hand-chased silver symbols such as a heart, a skull and a tree stump. Each will be adorned with different semi-precious stones.

Sotheby's has put a pre-sale estimate of 30,000 to 50,000 pounds on the charity copy, which will be decorated with moonstones, but observers predicted that the book could easily fetch 10 times more.