This is a work without peer. I see that some people have included in their criticsms below that it's "too bulky", it "doesn't have enough photographs", "it's not a travel guide", "it's not ordered by geographical area". It's an ENCYCLOPAEDIA guys, and doesn't claim any of those things, and if "bulky" is a criticism, due to the massive amounts of interesting information it obtains, well... (its format is actually as compact as is reasonable, I would say, and frankly encylopaedia-sized).
Also there are a number of references below to errors, none of them substantiated - not one example is given. I've had the first edition since 1983, refer to it often, pride myself on my knowledge of my native city, and have yet to find ONE error - though I don't doubt there are inevitably some, given the scope of the project.
If you want what it says on the cover, and what is an absolutely definitive and fascinating reference to London and its history which can be dipped into again and again, all in one place rather than relying on myriad web searches, then this is it. Yes, we've all come to expect hyperlinks these days, but this is a book so you just have to follow the cross-references! And no, I'm not related to, or known to, the authors/compilers :)