It was a Brantly 305, G-ATSJ.
Registration history from G-INFO - suddenly had an epiphany.
It was in the hangar when I started there in late 74, and festered there for years. Eventually was sold to goodness-knows-who and it disappeared by road.
A brief report of its demise is in Veeany's site
here.
It's funny, but I remember it being in that hangar for longer than it evidently was.
G-NEWS
Whether this was the black 206 to which PC refers I do not know
NEWS was a very dark green, easily confused with black at a distance.