Members of the BMFA, SAA, LMA and the FPV fliers have known of this for some time and will have been registered for over a year. Basically as long as you are a member of one of these organisations and registered there has been no change in the rules for fliers as there is an agreement with the CAA. Brexit has nothing to do with these rules as the UK was already committed to the EASA rules. Even in the EU each individual country is able to make their own allowances for model fliers.
Jim