Richard, it would have been built by Bristol Commercial Vehicles Ltd - one of the last, in fact. I believe A686KDV was numerically the highest built by BCV.
Some people seem to get upset about Olympians being referred to as 'Bristols', but BCV was owned by Bus Manufacturers (Holdings) Ltd at the time, and BMH was jointly owned by Leyland and the NBC, with a 50:50 split. the factory in which the chassis was built was owned and operated by BCV, so it's correct to refer to the vehicle as a Bristol. Similarly for Fleetlines built after the transfer of production to Leyland, can correctly be refrred to as Leyland Fleetlines, even if they have Daimler badges.
Nigel