You live in London or are thinking in a travel to there, it's always good know some local expressions and words. The Cockney rhyming slang: London slang dictionary has many local expressions to help you. Or read it just for fun.

But if your problem is with some classic Victorian Book, maybe Dickens like one of my friends, there is How to Speak Proper. My English is not good enough to catch all the meanings and expressions, but I liked those two links. They are useful and fun. (via growabrain)