Brexit not at fault
The largest problem facing GA in the UK has nothing to do with leaving the EU.
We need to look closer to home and see what is happening to the actual 'facilities' that are either being reduced or becoming too expensive, or to complicated to use.
Most of the 'Airfield Issues' that are now upon us are regulations imposed from the airfield owners and nothing to do with the EU.
When places like Biggin Hill are actively making it difficult to operate a club, and also require 'schedule like' permission just to go flying then that is where the worry is.
There is also going to be a decided lack of licenced engineering availability as there are precious few new comers (that will take licences) in the system to replace the current people that actually 'sign off' the GA fleet.
Luckily we still have the LAA in place to assist the enthusiast, however they do not operate airfields so can not help on that front.
We have 'lost' a number of what used to be 'usable' GA facilities and very few if any new ones will be forthcoming. Much of this is due to 'developers' getting control and then 'squeezing' the users, and of course GA is not a 'Vote Getter' for any political party.