Thanks Noyade for the fascinating response. I hadn't any idea that the turrets operated in that manner. I feel, however, that the system i was trying to describe is an air duct of some sort. Perhaps it was a crew/equipment heating system; the duct obviously passes into the wing root. There was a grub screw that operates from within the cabin which allows the flow of air to be regulated (I fiddled with it!) It strikes me as possible that the air is ducted to the nascelle of the inboard engine which supplies the heat.
Perhaps it blasted hot air into the equipment in the cockpit to prevent freezing problems.
Wild guesswork!
Put me out of my misery before I pay for the Haynes Manual.
Chf