If we are talking here about the UK only, I would put Prestwick high on the list. Going back to the 1940s, it has served as a transatlantic stopping-off point, it has long been in effect a dual civil and military airfield, it served as a diversion airfield when other places were fogbound, it was a manufacturing and maintenance site and many airshows have also been held there. So, while the volume of movements has probably been generally low, it must have seen a great diversity of civil and military types over the years.