Oven Heats up when switched off?

I have a New World 110 Dual Fuel Range Cooker
The electric fan oven top element is getting warm at the back of the oven when it is switched off at the control switch. Any ideas what's wrong. (It's obviously costing money when on)
I've tried to take off the top to check the switch but can't work out how to remove the thin strip that hides the joint in the middle of the top cover which is in two halves.