Just to let you know that I am awaiting delivery of a replacement magnetron. If I get stuck with it I'll let you know.
I have changed the magnetron over but I am getting an E7 error code. The magnetron fan is fine it seems though. According to the manual that code is for the magnetron overheating.
After a bit of fiddling with the magnetron cut out all seems to be well.
Thanks for your help.