the earth is good. New 50m run of 10mm2 SWR to the junction box which is
0.5m from the incoming (electricity company) 3 ph meter. Tested when
installed a couple of months back

50m from the house with an exported earth rings a few alarm bells, although
I doubt you'd ever get enough potential difference between it and local
earth to cause a shock, unless your house is built in a "difficult"
location, such as on a granite clifftop.

Christian.