Originally Posted by
DCflyerAA-YX
Wouldn't the OP have to reclear immigration?
Doing the initial connection from flight A to flight B there is no immigration, so getting to the lounge would avoid this. But leaving airside T3 at any stage means passing the UK Border and therefore a passport check. Re-entering T3 later that day would not involve going through passport control.
Originally Posted by
Deltus
Is there no "Ready To Fly" equivalent at T3, like there is at T5? Could one merrily walk round the loop and re-enter security multiple times without raising any eyebrows?
No, HAL have something called Positive Boarding to control entrance into T3 but it has nothing like the functionality of Ready to Fly and it's not even mandatory to be registered on it.