Belling Gas – Issues with cutting out

Having issues with a Belling XOU60G MK2.

Everything works fine but after a period of time (poss over an hour) the oven seems to cut the clock out which obviously stops the cooker from working. My initial reaction was maybe the cooling fan wasnt working and the top fascia was getting too hot which failed the clock. Is this the/a likely scenario?

Other details
Units around are fine, plenty ventilation.
Does the fan only start when the oven is actually on (heat) or should it cut in when you are attempting to start the oven?
If it is not the fan then what else could this be, PCB, Therm Cut-Off?
No evidence or burn or smolds internally.

Basic background – Oven was in a house I rent out and I swapped it out for an elec one once it started playing up. I now have this oven in my house and want to get it up and running before paying someone to run the bayonet clip into the gas pipe. Hence the question about the fan starting, I have no gas supply to the oven so cannot varify if the fans actually works.

Any help would be greatly appreciated.
Regards