Wright said the images were completed in 1998. "The images are part of a series of 10 which were sent to the publisher Bloomsbury as rough ideas for character development and composition," he said.

"Each drawing was submitted by fax and returned with comments. The designs were also passed on to JK Rowling for her approval and any comments passed back to me.

"On deciding the look of the characters and the picture composition, the watercolour illustration that you see on the cover was then completed, and when the book was published in the autumn of 1999 it became a global phenomenon."

"Thus, for example, the hippogriff was based on a design that was sent through to me from Jo. Along with griffins and dragons, hippogriffs can be found in medieval bestiaries."