Two days ago I flew JFK-AMS-LHR arriving into Heathrow's Terminal 4. The fact that KLM seemed the only other airline operating there, in addition to BA, got me wondering... Why is that? Why doesn't KLM operate into the other terminals, like the other major European airlines I saw?
Also, I noticed in the underground that a sign directed you to LHR's T1,2,3 or T4 depending on your airline. In the case of BA, depending on your long haul destination, the subway station is different. Why does BA split its l/h operations? Is it only a matter of capacity, or there are other reasons? And was there a specific criterion to assign flights to either terminal?
Anyways, the whole thing seemed weird and got me wondering. So I thought someone at a.net might know.