Hi David,
It sounds like the element has gone - switch it on again and double check the heat. It will give the impression of only getting warm when the element first goes because its just warm when you realise the oven isn't cooking.
If you require an element you can get one from us - the one you need is here, copy and paste in to your browser:
http://www.ukapplianceparts.com/elements.asp?search_fd5=B1421
Make sure you power off before repair:
1. Remove the back plate from inside the oven 4/6 screws - this will expose the element and fan blades.
2. Remove 3 screws holding the element in place.
3. carefully remove the element taking care not to pull of the wires until the element is free.
Lee
January 2007