Reddit mentions of Hedgerow: River Cottage Handbook No.7

The Forager Handbook by Miles Irving is very thorough in it's number of edibles, but not fantastic to carry around or for ID. I combine it with The Wild Flower Key by Francis Rose. I pick a couple plants from the Forager Hand book at a time and look for them on a walk.
Another book is the River Cottage Hedgerow by John Right, in fact all three of his book are well done; Mushrooms and Edible Seashore.

https://www.amazon.co.uk/Jekkas-Complete-Herb-Book-Association/dp/1856267415/ref=sr_1_3?s=books&ie=UTF8&qid=1504455888&sr=1-3&keywords=Jekka

https://www.amazon.co.uk/Preserves-River-Cottage-Handbook-No-2/dp/0747595321/ref=sr_1_1?s=books&ie=UTF8&qid=1504455955&sr=1-1&keywords=pam+the+jam
https://www.amazon.co.uk/Hedgerow-River-Cottage-Handbook-No-7/dp/140880185X/ref=pd_sim_14_2?_encoding=UTF8&psc=1&refRID=F3VYXKB4NNCVEYAJEQ0K
https://www.amazon.co.uk/Booze-River-Cottage-Handbook-No-12/dp/1408817934/ref=pd_sim_14_5?_encoding=UTF8&psc=1&refRID=2YHRTEAT811G23JYQSDR

I love these ones as they give you a target to go out and find stuff. They'll have links to other books that the authors use. All three are the best in their field(!) on foraging and using foraged items to make wondrous delights. Yesterday I also picked up
https://www.amazon.co.uk/Hedgerow-Cookbook-delicious-recipes-wild-ebook/dp/B00PPHWYNO/ref=sr_1_1?s=books&ie=UTF8&qid=1504456311&sr=1-1&keywords=The+hedgerow+cookbook

Many of the edible weeds in N. America are also found (or have edible counterparts) in Europe also. Things like dandelions, dock, chickweed, and amaranth are all common.

Most seaweeds around the world are edible if you are going to be on the coasts.

I'd take a look at these books from Amazon's UK site as many of the plants will also be found on the mainland too:

Self-sufficiency Foraging

Food For Free

Hedgerow

Edible Seashore

Hey there friend! You've got plenty of responses and they're all good :). Just a quick few bits from another UK forager (wasn't too long ago I was in your shoes).

Might be worth investing in a book just to get a general idea of what's around in Britain. "Food for free" is great, but a little large to take around. Good for those cold cold nights and nothing's on TV/a good reference book.
https://www.amazon.co.uk/Food-Free-Richard-Mabey/dp/0007438478

The one I really like is River Cottage Handbook hedgerow which most of UK non mushroom stuff revolves around. Excellent read, funny informative and great photos. I've met John Wright and he really is an awesome and fun guy. Lots of great tips on what to do with the stuff you find. Also good combined with Jam and Preserve making book, which has masses of recipes to keep your foraged goodies lasting all year round. The hedgerow book you can just about fit into your jacket pocket - if it's a big one that is...

https://www.amazon.co.uk/Hedgerow-River-Cottage-Handbook-No-7/dp/140880185X


https://www.amazon.co.uk/Preserves-River-Cottage-Handbook-No-2/dp/0747595321/ref=pd_lpo_sbs_14_img_0?_encoding=UTF8&psc=1&refRID=58P3VRK2HZ8Y4ZY2N43K

After that maybe check out any local foraging groups or classes? Depends how much you enjoy it. If you're anything like me, then you're in for a real treat :).

P.S the most important bit of any book is the dangerous/deadly section. Make sure you can recognise the nasties or at least not pick anything that looks remotely like them until you're 100% sure and confident!