+1 and lesson learned.

I assume your aware that on metal control the 0v are tied to metal cabinet

The 0v shouldn't be tied directly to earth this would be an earth fault.

Measure resistance between Earth and 0v on a dead panel, nothing.

Measure DC from 12v to Earth, nothing.

Its was not a metal control panel.  I did all this measuring things to earth.  There was nothing detectable that could be considered a fault. I did all the checks to test the cabling from the consumer unit to the spur.  As I said previously, there was no faults or anything detectable at the moment I did the test. I methodically tested for every possibility but nothing could be found.  If the problems intermittant it won't be there when you test unless you are lucky. The problem was some thing intermittant to do with the mains supply. I methodically proved it by pluging the panel into a 13 Amp socket for 48 hours.  There was no fault.   Soon as I connected the panel to the spur the fault started after about 20 mins.   There electrician rewired the spur back to the consumer unit.  The fault has now gone.  It was there faulty cabling / spur or what ever.  But when I tested it there was nothing detectable.

The fault has now gone.

Yes I did read the full thread. This is regarding my quote.

Quote ?

The 0v shouldn't be tied directly to earth this would be an earth fault.Measure resistance between Earth and 0v on a dead panel, nothing.Measure DC from 12v to Earth, nothing.

??

So how do you account for earth loop faults then?