It was indeed a spurious AAPP fire indication, the cause of which has been established. The aircraft has had a Rover wash and was fired up today - all was fine.
So, a quick romp around the compass base (nothing like the old MFS/HRS swings as the aircraft now has a much simpler system to befit the VFR-only role under which flights will be conducted), then a trip back to Bruntingthorpe tomorrow.
Looking forward to seeing more piccies as good as Al R's - simply stunning, those were!