This book by an American born woman who has been transplanted to Britain is a very enjoyable read. Her anecdotal style makes the information fun and fascinating, and her insights invaluable, though one must have a sense of humor about both cultures as she is very tongue-in-cheek. As opposed to most other books I've read on the subject that are almost strictly technical, Walmsley tells the readers in a very conversational style about many differences that wouldn't occur to most travelers - differences in attitude (about sex, gender issues, finance, etc.), values, customs, ettiquette and habits; and she may sometimes touch a little on why the discrepencies exist.
Because this is in no way a dictionary style book, she does not offer alternate words, phrases or technical info. Thus, as a supplement, I highly recommend "Divided by a Common Language" by Christopher Davies, who (as opposed to Walmsley) is a Brit who now lives in Florida.
All in all, a humorous, anecdotal insight into two very different cultures. Even though this may not be as technical as some travelers would prefer, the information is crucial for developing a truer understanding than is offered in any travel guide, so do not pass it over for the latter; buy it as well.