Hi Ewan,
This will be your fan oven element that has gone. It is accessed from inside the oven - remove the back plate which will reveal the element and fan blades. It will then be apparent how the element is fixed - normally 3 - 5 screws.
A new one is availble here for your model:
http://www.ukapplianceparts.com/elements.asp?search_fd5=ZHQ575W
Be careful not to inadvertently pull the wires off when removing the element otherwise they may retract in to the rear of the oven which will mean that you have to take the back off the re-connect. Not difficult just a lot easier if you can avoid it.
Lee
January 2007