I'm not sure what's available in the UK, but amazon
has a lot of books on A&P, and there are usually a lot of good reviews for each title.
As far as nutrition books, I got The Horse Nutrition Handbook
by Melyni Worth, and I love it. Here are the chapter titles: Basics of Equine Digestion, All about Nutrients, What to Feed and Why, Designing a Balanced Feeding Program, Feeding for a Lifetime, Feed Storage and Feeding Tips, Pasture Management, Diets for Common Equine Disorders, and Appendices. There is a lot of good information in there, and all the formulas are given in metrics.