Well, it's loosely based on Patrick Hamilton's novel Hangover Square which takes place in the seamy Earl's Court area of London. Hanover Square is in posh Mayfair. I can't find any reference to a change of name - Halliwell usually gives these (e.g. Out of the Past became Build My Gallows High in Britain), but there's no mention of one in his article on the film or the list of name-changes at the end of the book.