One of the principal arguments put forward by the CAA for increased transponder carriage by GA was a 50% increase in air traffic movements by 2020 which was projected in a Government White Paper published in 2003. That was an increase in commercial traffic, not GA/Gliding.
The newsletter of the Association of European Airlines dated 3rd June rather knocks a hole in that "increased traffic" extrapolation. Stagnation, reduced passenger loads and gloom seems the real current picture. See
http://files.aea.be/news/pr/pr08-019.pdf
I suppose because it appeared after the expiry of the CAA consultation period on 31st May, it won't be counted in the argument