Hotpoint oven tripping problem returned?

I thought I'd solved this but the problem it has returned.

Had problems recently with the top oven of our double hotpoint oven tripping the house circuit breaker. Found one of the grill elements had gone. Replaced that and everything was ok for 2 days. The problem has returned. What ever the problem is it is caused by the first part of the switch rotation. If I turn the power off and select the temperature I want and then turn the power on it is fine. It happens if I turn the switch from zero with the power on. If I disconnect the element that doesn't trip the circuit breaker when I turn the switch.

Any one any ideas? Don't want to admit defeat and pick up the yellow pages, but I might have to.