No longer allowed to mix CTA arrivals with International arrivals. Think this has been going on for a while, they don’t even have a domestic channel at Gatwick South, which for an airport which has greatly improved and has high ambitions, is one hell of an oversight.
Used to get a ticket on arrival which allowed you to bypass the passport check, then later a boarding card was all you needed for staff to waive you through. The issue seems to be there were mixing in with arriving international passengers, hence this was fairly open to abuse.