I can't speak for the UK at all, though I can say that in Canada, there has been a visible reduction in "activity" at the smaller GA airports since I started flying in the mid '70's. The flying club where I learned to fly was, and remains one of Canada's most active. They are the only flying club in Canada to own their own airport, which is very nice. During my training, if the circuit got too busy, they would simply close the airport to non members for that part of the day. I'm not aware of that happening in recent decades. I stopped in there on a very nice day last summer, there was activity, but nothing like what i had remembered from earlier times. Other local airports are quiet of even closed, though the remaining airports can handle the more compressed "fleet".