Hi Romany,
Have you been to Borders in Fforestfach ? I was there recently and they have a great selection Photoshop books. I have just purchased' Creative Photoshop Lighting Techniques' by Barry Hughes and 'Photoshop CS Studio Techniques' by Ben Willmore. I also have Adobe Photoshop 7.0 for Photographers by Martin Evening and Photoshop 7 for dummies amoungst other titles.
It depends on what area you want to focus on...An all round good book for Photography techniques is 'Adobe Photoshop 7.0 for Photographers' it has great tutorials as well as insight into various techniques, i would imagine it is more than suitable for your needs.
I would also recommend 'Creative Photoshop Lighting Techniques' as it has grea examples of the different uses of lighting as well as a well written section on all the lighting setting, i have found this book totally interesting.
Dont forget the Retouching book by Katrin Eismann but they dont currently have it in Swansea, and as i dont own the book yet, i you may find this thread helpful.
http://www.retouchpro.com/forums/forumdisplay.php?f=46