I'm new to the selling lark, and want to set up a shop to sell a book that I've written
It seems a little extreme to have a shop if you're only selling one book, you need 50 listings to break even on the fees as a business seller.
http://pages.ebay.co.uk/help/specialtysites/questions/open-store.html
As it is a book that you have written, you would be required to register as a business, inform HMRC and be conversant with the Distance Selling Regulations.
It might be a good idea to visit the Business Seller Board for more information
http://community.ebay.co.uk/forum/Business-Seller-Board/1900001545?