The area around Oxford seemed to be the busiest on FR24 when I was looking. The Vans RV's were numerous and also the Ikarus C42. Also a couple of Sport Cruzers which has to be one of the sexiest of the new breed of aeroplanes.
Plus a good sprinkling of Cessna and Piper spamcans pottering around. Sadly as SSD points out, these are generally quite aged and yet still form the backbone of the training fleets.