I haven't read the whole thread, but -
to find earth leakage, the Line and Neutral of various circuits are clamped; not the CPCs(earth wires) or bonding conductors.
You need to find out where the earth leakage is originating, not where it is going.
Thanks for the reply. I've unplugged everything that can be unplugged and still seeing around 100mA when clamping at the meter tails but haven't had a chance to delve deeper at this time. Just wondering if moving the main earth from the spike in the ground to the water pipe, as a temporary measure, might improve safety.
Regards Stuart