Okay, this is dumb. As pointed out by BoingBoing, a 17 year old boy has been arrested for possessing The Anarchist Cookbook, a book that is readily available from amazon.co.uk.

It’s also not a very good manual on making explosives, according to one of the reader reviews-

This book is very informative as to how to get yourself killed. Being a student of chemistry i can safely say that THE RECIPIES IN THIS BOOK ARE VERY INACCURATE. It’s more of a good read than an explosives manual, if you want to make a bomb, look elsewhere.
On the whole a very good read, but don’t take it seriously.

Somebody buy a copy and send it to West Yorkshire Police as a gift. Maybe then they’ll get a clue.