Another data point. Doing a return to Dublin today to start an ex-DUB itinerary I arrived at the 200 gates on BA0834 at 1150. Very quick to immigration but I got there half way through what looked like a 747 sized crowd (but obviously wasn't) decanting into the area . Took about 7-8 mins to get through the queue. I'd have been getting nervous if I'd been on a back to back (which I will be in a couple of weeks).

The departures hall with the check in desks also has building works so hoardings and queues can slow progress back to security.

Giving serious consideration to changing my future B2B flight even though its the end of an itinerary rather than the start so not as crucial.

Question: Who qualifies for fast track security - I was in CE but nothing was on the boarding pass?