but then it is the CAA
EESDL - perhaps some praise for the CAA is really due because they publish annual fleet stats which gives the total fleet in weight categories. The categories are 0-750kg, 751-5700, 5701-15000, and then they split it out by CofA/Permit category. The total at 1st Jan 2016 was 1258. See
Aircraft register statistics | UK Civil Aviation Authority