I have taken secondary school kids to London for the past eight years now (being a teacher of English from Holland) and we never skip Declan's Blood and Tears Walk during our school trips. He is a wonderful tour guide, and my pupils always think he is one of the highlights of their trip to London (and that's saying something, since 16-year-olds are notoriously uninterested in just about anything we, the teachers, suggest is fun :) .
This book is a sort of pocket-version of Declan: the stories are short, simple, gripping, well-described, and you can actually do a sort of Blood and Tears Walk yourself with this book in hand (there's maps to the sites in it), but it talks about many different things than the live tour in London. I highly recommend this book if you're into London's dark past. It is very well researched and you'll come away from reading it feeling like an expert on horror yourself! I also highly recommend Declan McHugh's Blood and Tears Walk: if you're visiting London, go and do his walk. You won't be disappointed.