chris French wrote:

I don't think it's that uncommon Andy, it older properties not recently
rewired. Our last house - 1938 semi, some wiring done in the 1960's ish
probably, but still old rubber stuff on the lighting circuit.

Our only earth was via the lead water main.

Yes, I've never doubted that that used to be quite common practice.
OTOH confusion has often arisen between the earthing conductor and the
main bonding connection to the water service in threads such as this in
the past, hence I felt that the possibility should be considered and
eliminated (or otherwise) at an early stage in the discussion.

--
Andy