Would you recommend a C3 for no visibility of the earth spike/plate?

It is certainly a matter for further investigation.
Depending how you measured that 70 odd ohms the installation may be relying solely on something not intended to be an earthing facility such as an external  water or gas pipe, that may be interrupted at any time by some unlucky plumber or gas fitter. They could then find themselves painfully or even lethally in series with leakage currents from the house. There has been the odd plumber electrocuted while changing a stopcock.

If however that was a test result with bonding and final circuit CPCs removed, then presumably there is a wire to an electrode somewhere that may be totally buried, and that may be OK.

very hard to say without seeing it.

The 'if in doubt' option is probably to recommend  a new electrode in parallel.

Mike

Agreed with Mike. It could be hidden in a flower bed behind a wisteria or whatever.

Not C3 for me - either it exists (no code) or it does not (at least C2) so as Mike says, all depends upon functional testing.

Agreed with Mike. It could be hidden in a flower bed behind a wisteria or whatever.

Not C3 for me - either it exists (no code) or it does not (at least C2) so as Mike says, all depends upon functional testing.