Sam McBride: So long, Common Travel Area? Why centuries of free movement between Britain and Ireland could be about to end

I’m writing this at 30,000 feet, somewhere above the North Channel between Belfast and Heathrow. A few minutes ago, I showed my passport to board what is a domestic UK flight, but the Common Travel Area (CTA) means I could have got on in Dublin and shown only a driving licence or some other form of ID.