Overheating problem with John Lewis oven

We have a John Lewis JLBID0911 built-in oven, bought back in 2009. Until last night it’s been flawless.

We were cooking a curry and the final item was a Naan. It was cooked on fan at 200C. At the end, the oven was turned off at the control panel and left to keep the Naan warm while we dished up.

However, although the fan and light turned off, and the control panel indicated it was off, the rear heating element stayed on. Of course, it got extremely hot and was glowing bright red. We noticed it because when we removed the Naan, it was scorched.

Like I said, turning the oven off made no difference. We cooled it down by switching the oven back on and setting it to 30C fan and left the door open. We then isolated the oven.

This morning, I put the oven back on and set it to warming (top and bottom elements 80C). All OK. Next was fan at 100C. Again, all seemed OK, but when I switched off, the rear element stayed on.

Any ideas? Can this be fixed or is it a write off?

Gareth