Originally Posted by
KARFA
Gates are usually posted around an hour before the flight, although if you ask a BA agents when they are checking your bp they should be able to tell you before that what the indicated gate is - albeit there is a small chance it may change prior to it being displayed.
Long-haul flights do generally get their gates posted about an hour before takeoff, since extra time is needed for document checks, extra screening for flights to the U.S., and for boarding in general. Short-haul flights usually don't get their gates posted until much closer, typically 30-40 minutes before departure. One reason is that LHR makes a lot of profit off shopping, and they figure if people know they won't have a gate for another 45 minutes or so, they will shop.