The original meaning 'within the sound of Bow bells' is an antiquated description when London was an extremely small city. You cannot call yourself a Cockney just because you happened to be born at Barts Hospital five minutes up the road. Its now used to describe any working class Londoner with a so-called Cockney accent. The accent has probably disappeared as well in the true sense if you listen to the accents which were derived from it, such as Basildon.