You could also try the Rough Guide series or the Lonely Planet for UK.
The former is English and the latter Australian while the Lets Go is
American. Take your pick. They are also excellent for finding out about
good transport and museum deals. There is also the web-friends of mine
have actually booked very cheap and reasonable accomadation in the
US from Africa via the web. You might want to look a bit outside
London-on a rail or tube line because places in London are very
expensive-even youth hostels.

Enjoy your visit
Kathryn