I think I have resolved the issue.
I have borrowed a multimeter and traced the fault to a burnt out cable in the wall switch.
Not sure why this has burnt out so for now will replace the cable from the wall to the oven.
Not sure why the temperature neon came on as I assumed power was OK.
If the cable burns out again I will need expert help.
It was the neutral wire from the switch to the cooker.
It has also damaged the switch so I shall replace that.
I was thinking of doing that with the wire.
I have just noticed that the wall switch was just a 13amp fused spur. Probably was OK but I will replace with 45amp switch.