The original preparatory Prisoner of Azkaban sketches drawn by artist Cliff Wright will be up for sale at the 14th annual Glasgow Art Fair. The first drawing featuring Harry and Hermione on Buckbeak the Hippogriff will be up for sale at £13,000. The second sketch features "The Grim - a dog-like omen of doom." It will be put up for auction at about £11,000. These were used as the basis of the UK cover, which you can see the standalone image at his website.

Illustrator Cliff Wright said of his Hippogriff drawing: "The image is one of a series of 10 which were sent to the publisher Bloomsbury as rough ideas for character development and composition. The designs were also passed on to JK Rowling for her approval and any comments passed back to me. Thus, for example, the Hippogriff was based on a design that was sent through to me from Jo."

A previously unseen sketch for the third Harry Potter book will go on sale today in London for 8,500 pounds sterling. Art experts estimate that the lucky buyer could re-sell the coveted piece for a five-figure sum.

The sketch's illustrator, Cliff Wright, who also drew the artwork for Books 2 and 3, commented: "In some ways I prefer the sketch to what ended up on the cover. It's more dynamic: in the final version, the hippogriff is not moving quite so fast. JK Rowling herself faxed over an image of what she thought the hippogriff should look like."