By the way, it is not quite true that an RP accent will disguise your origin. Rather, it marks you out as a member of the aspiring and well-educated middle classes, most probably from the Home Counties.
Recently, I watched some episodes of an old British sci-fi show called "Blake's 7", and -- as was normal at the BBC in the 1970s -- everybody spoke with a lovely PR accent. That was fine for some of the characters, but hearing Gan speaking like that was very strange. Gan was a big but uneducated strongman, but he spoke like Prince Andrew -- it simply didn't fit his character.