THE author of the Harry Potter books has performed her own personal conjuring trick.

Joanne Rowling, better known by her initials J K, does not have a middle name, according to her birth certificate. The use of the author's initials instead of her full name was a marketing ploy designed to make her work acceptable to boys, who actively choose not to read books by women.

Yesterday, her birth certificate, published by a Bristol newspaper, shows her parents registered her as Joanne Rowling. Her publicity agents have said her full name is Joanne Kathleen Rowling.

Rowling was born on July 31, 1965, at the Cottage Hospital in Yate, near Bristol. On Aug 23, 1965, her mother, Anne Rowling, registered her birth. But the certificate shows the child had only one forename and the only other details on the certificate concern her father Peter John Rowling who, in 1965, was an apprentice engineer.

Rowling could not be contacted yesterday. Bloomsbury, the publishers of the Harry Potter series, said the author took her grandmother's name. A spokesman said: "Clearly it was not her name given at birth but it could have been her confirmation name. When we asked her for her initials, she said J K."

She added that the publishers decided to use initials instead of a name to attract boy readers. She said: "As it happened the first book was such a success that within two months of publication she was on Blue Peter, so it was blown. There are many examples of authors changing their names."

Commenting on the use of her initials, Rowling said in an interview: "It was the publisher's idea, they could have called me Enid Snodgrass. I just wanted it [the book] published."