Yes, you are right re the keg beer push and, of course, the lager revolution.
I joined Bass in 1973 and it was during part of my induction that I saw the cask Worthington E in the Burton on Trent Brewery and coming from the south of the country, I had never seen cask E, only the keg version...
Have just been trawling back through this thread and as a point of interest, I can remember Worthington E being available, in northern parts of the old Bass empire , as a cask beer. From memory, I think it was similar to draught Bass, but without dried hops being added to the cask last thing as...