Where you at Toby??? Aussie perhaps???
From your description it would appear that the oven flame failure device is faulty or you have a possible open circuited solenoid coil feeding the oven from the gas valve. Undertake an electrical test on the solenoid coil and check it out.
I was not aware that Chef ever manufactured a cooker with glow plug oven ignition and I have repaired many hundreds of their cookers – even my service manuals do not show a model as you have explained – how old is this unit??? any idea???
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians