The spike was fitted by an electrician.
The advice to fit a spike came from Naim (via the dealer), not from Russ Andrews, although I did ask him if it would be ok and he said it would be "fine" as long as it was fitted by a qualified electrician.
The advice from Naim was:
"Use a dedicated earth for the sockets. Use the house earth to protect the cable run, but don’t connect it at the sockets. Get the sockets’ earth from a totally separate rod outside the house. The rod should be as close as possible to the sockets, but needs to be somewhere where the ground doesn’t dry out too much."
Then Keith you should have a certificate with your house documentation to say your utility supply is now (or was) configured as TT. Please check you have that or obtain from your electrician... if something goes wrong your insurance company might need to see that. A properly situated and installed electrode will be provided so environmental variations have minimal impact (suitable depth in shaded location with good local ground conductivity) , and certainly not require user intervention to keep moist (would need to be salty water BTW).
Also note a single electrode DOES NOT remove most RF from the mains, it now allows you to add an additional RF sink set of electrodes safely. If in doubt discuss with a CEPT class 1 licence holder (happy to do this off forum).... electricians don't need to study this or be examined on this in the UK. Earth electrodes utility specifications in the U.K. are for safety and NOT RF... that is covered separately.