Thanks for the advice. I do feel better now about putting the cooker back into service with what I considered still rather poor insulation resistance even after repair.
I checked the cooker wiring with the elements disconnected and that was fine.
There was no external evidence of a hard fault on the element I replaced, but it tripped several times during warm up, not at switch on, and worked OK on a non-RCD circuit.
Anyway I've discarded it now.
I'm still surprised at the way the insulation resistance drops so dramatically as the element warms up, even with new ones.
