"Certainly not in our UK wiring system, where mains ground is ground, and NOT from the re-used neutral conductor relabelled."

I'm not quite sure what you mean by that, but in my house there is no separate earth. The 'earth' wiring is connected to the neutral at the fusebox. As I understand it an RCD trip then prevents an earth leakage fault in my house from frying me, but does not prevent a fault outside the house from making my plumbing live. This system is called PME (protective multiple earth), apparently.

I have never understood why the 'earth' (ie neutral) is connected to the plumbing when the water enters the house in a plastic pipe.