The food has now been eaten and I have defrosed the FF. I removed the
back of the inside of the freezer section and then removed the
polystyrene and the metal cover from the cooling fins. I found that
there was ice covering up the return air duct. Defrosted with a hair
dryer, put it all back together and gave the FF a good clean. Repowered
and it is now working fine.
The only remaining question is why the ice was there in the first
place. If the problem re-occurs in the near future I suspect that the
fault will lie with either the defrost timer or the heating element.