In message , Andy Wade
writes
dave wrote:

The house is a 50's semi. Earthing is provided by a conductor bonded
to the cold
water supply where it enters the house. There is an RCD fitted in the
CU. Both
rings and lighting circuits have mcb's.

Are you sure you're not confusing the "means of earthing" with the
(required) main bonding connection to the water pipe? Is there any
other connection to the main earth terminal? Is your supply from an
underground cable, or overhead wires? A photo of the supply intake,
meter and consumer unit would help if you have a digital camera and
some Web space.

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.
--
Chris French