I was able to change the tube but it would not light fully so I was looking for the starter. It was not in the vicinity of the controls but I spotted two wires running to the back of the oven. I pulled out the oven and opened up the back panel and the starter is located just above where the mains cable is connected. You have to remove the entire back panel which is just a few small screws. Obviously ensure the oven is properly isolated from the mains before attempting this and it needs two strong people to lift out the oven. The front doors can be removed to reduce the weight a little.
Peter Carroll, April 2021