UK Appliance Repair Questions? Ask a Technician for Answers ASAP
It's not your timer at fault. More likely to be the circular element in the oven.
Isolate the supply to the cooker.
Inside the oven, remove the 4 screws (maybe more) holding the back plate on, take the backplate out to reveal the element.
If you are lucky you will just have to take out the screw(s) holding the element in place, then, carefully bring it into the oven with it's wiring attached. Transfer the wiring to the new element and refit to the machine. Refit the back plate and your oven will be fixed.
If you are unlucky, you'll have to take the oven out of it's housing, remove the back panel and take the securing nuts off the element.
Hope this helps