Oven temperatures just keep increasing?

I have a Stoves cooker (#059040423) that has worked flawlessly for the past 12 years.

Now though, the oven just keeps getting hotter and hotter, regardless of the dial setting. I noticed that one end of the thermocouple was hanging out of the bracket, so have clipped it back in, but there's no change in the behaviour.

Do you think a new thermocouple will do the trick, or is it likely to need a whole thermostat?

Cheers,

Mike