Originally Posted by
flyinbob
I think it actually has to do with the immigration and customs officers, and UA not paying them for one remaining flight. UA personnel are around regardless of which terminal. But ICE people are there primarily in the AM for arriving Asia flights. If the LHR flight is late they do switch to TBIT.
That sounds like a more plausable explanation: ICE is the one who doesn't want to pay people to hang around and they care far less about giving pax a hard time.