Belling 629 SS blew fuse – now won’t turn off

Happy owner of a Belling 629 SS for the last 13+ years. Have had to replace a couple of elements along the way and a few bulbs but that’s it.

Yesterday, at the back end of a slow roasting session (8 hours use), I closed the oven door and it tripped out. Flipped the fuse switch and it tripped the whole house out this time. Left it to cool off for half an hour and then flipped it back on again. This time it came back on without tripping anything, but the oven would not switch off despite the knob being turned to zero. I’ve had to turn it off at the wall.

I’m no electrician, but my gut tells me there’s a thermostat issue somewhere. Any advice? I’d like to have a go at fixing the old girl.