The bottle opened this week is from Devenish Brewery. It was presented in a 275ml brown bottle with foil top. It was the first one that I have opened that has any sort of sparkle to it with a comforting pfzz on opening and even a small head when poured. The beer was a ruby red colour and poured completely bright.
These beers are generally not tasting too good, and would be generally considered to be "stale". However the sparkle did give it a lift and through the cardboard flavour and aroma did come some sherry/madeira notes and a hint of toffee/caramelisation.
Again no suggestion as to strength as that was not required to be on the label thirty years ago. Failed to drink the whole bottle.
Good Beer Guide 1982 suggests that there were two Devenish Breweries in 1981, one in Weymouth and one in Redruth. The bottle gives no clue as to its provenance. About 100out of their combined 360 pubs served real ale at that time.
Century of British Brewers published by Brewery History Society suggests that brewing ceased in Redruth as late as 2004 and in Weymouth in 1985.
The pubs were taken over by Boddingtons in 1993 - part of Whitbread's consolidation of the British pub and brewing industry. The pubs I believe, though cannot be absolutely sure, eventually found their way into the Punch Taverns estate via banks and venture capital investors.