Hi Pete,
This is most likely your fan oven element that has gone.
Power off before repair - the repair can be done on this oven in situ:
1. Remove the back-plate from inside the oven; 2/4 screws.
2. This will expose the element and fan blades.
3. Remove the screws holding the element in place.
4. Carefully remove the element so that the wires connected to it do not pull off.
5. Once the element is free remove the connecting wires and replace with an element from us here - copy and paste in to your browser:
http://www.ukapplianceparts.com/elements.asp?search_fd0=Fan%20Oven%20Element&search_fd5=ZHQ575W
Lee
January 2007