I suspect that even with the reduced number of flights, there's a substantial change in passenger flows at T5. BA used to be a network carrier with substantial numbers transferring from short-haul flights to long-haul (and vice versa). With virtually no long-haul operation, T5 is going to be primarily O&D, which will mean substantial pinch points at security (as opposed to the FCC), and I would imagine inbound at the border as well, particularly with no more eGates. Hopefully HAL can move some staff around, and bring back more when necessary - it looks pretty rubbish at the moment.