Fault finding weird issue

[HappyHippyDad]

update us @Georgemidnight when you discover the problem (even if it's something silly you've missed, we all make mistakes). We'd all be interested to know and it's mildly frustrating when you don't get closure.
What are your new IR results since you put your new leg in? Also, what are the IR results between (L-E, N-E or L and N combined to earth)?

 

[Marvo]

No, it stays livened up until any piece of equipment is plugged in.

I am a qualified electrician come here for advice.

Unlike an OCPD like an MCB, a residual current protective device won't trip even if there is a fault unless there's a load plugged in and some current flowing.