Really? The last time I flew AA from LHR there was a security check when you entered the departure area for your flight. That would be the "gate", imo.
Yes I am aware of that, I think perhaps the important part is that they don't ask you to take your trousers off. All gates at LHR T3 and the new pier on T1 (soon to be part of T2) have gate rooms and a boarding card check on entry, as do some of the gates at LGW North and most at LGW South.