You're not related to Fred Elliott are you Woodstock ?
I SAY. You're not related to Fred..................
The Johnny Jumbalaya Wild Food Guide is a good book with detailed descriptions of loads of plants. No photo's for ID in it though so it has to go hand in hand with a field guide.
the Roger Philips book is 'Wild Food' and it is a superb text. However, it most certainly is not a pocket book.
I would suggest getting a good pocket field guide on wild flowers/plants (like Larousse) to help in positively identifying the stuff in 'Food for Free' and 'Wild Food'.
For the UK, I don't think you need anything more than those two books to tell you what to look for and a guide to help you identify them.
I've found that other books tend to repeat a lot of the same stuff or just offer different recipes.