Should the earth connection for an outside garden rcd socket be derived from a local earth electrode rather than using the property's earth due to its location being outside of the equipotential zone of the existing property? The origin supply for the external rcd socket is protected by an rcd within the property's consumer unit.

What country are you in?

Not sure how it is "across the pond", but here in the u.s. you would just use the earth wire coming from the consumer unit. The only time you need to drive another ground rod is at a detached building that has what we call a sub-panel, a "sub consumer unit", basically a smaller consumer unit coming from the main.

You "MUST" maintain the existing earth or ground conductor... without it the overcurrent protection devices (fuses or circuit breakers) will not work.
Is this just a small circuit? Say 20 amperes or less"

What country are you in?

Not sure how it is "across the pond", but here in the u.s., you would just use the earth wire coming from the consumer unit. The only time you need to drive another ground rod is at a detached building that has what we call a sub-panel, a "sub consumer unit", basically a smaller consumer unit coming from the main.

Hi, Your answer does make sense and is how things are done over here! I just wanted some alternative points of view as this is often a topic of debate. Thanks for taking the time to reply; it is appreciated!
Kind regards,
Mike M...

you "MUST" maintain the existing earth or ground conductor...without it the overcurrent protection devices (fuses or circuit breakers) will not work.
Is this just a small circuit? Say 20 amperes or less"

Hi, Thanks for taking the time to reply. I'm currently using an armoured 3 core cable fed from a fused spur at the house to feed an RCD weather proof garden socket to power a fountain. Supply current is around half a amp but at 240v ac. There is some confusion as to the use of a separate earth stake due to the remote socket being outside of the houses equipotential zone? I currently use the house earth via the third wire in the armoured cable which seems to work well and provides adequate disconnection times!
Kind regards,
Mike M..