name='Steve Crook']London isn't a small area. It's bigger in area than many counties
Remember Professor Henry Higgins from Pygmalion (& My Fair Lady). He claimed to be able to tell which district of London (or even which street) someone came from by their accent, and it's not that ridiculous a claim. Maybe more so in his day, but there are still a wide variety of accents in London. Many of them do come from the person's family and ethnic bbackground but many of the accents used in the street or at school when kids are together are particular and peculiar to that area. London is really a collection of small towns and villages all crammed in together
Telling if they come from norf, sarf, east or west Lundon is easy, the refined and practised ear can narrow it down even more than that. Do they come from Dalston or Tottenham? From Wimbledon or Streatham?
Steve