The question of UK AOC was raised by Easyjet asking permission of shareholders earlier this month to amend the company Articles of Association. Shareholders formally voted it through this week - along with the CAA agreeing in all but name to grant an AOC to Easyjet UK. The chairman of Easyjet has gone on record saying Easyjet plc is now Brexit-proof. I imagine if the legal address of the company moves from the UK to Austria the details of Brexit might invalidate it for UK domestics. Getting a UK AOC for a wholly owned subsidiary rather than the parent company would remove some legal ambiguity - worth the cost of the insurance premium
Pick up a copy of yesterday's or today's FT if you don't believe me