Yes, yet another question about LHR transfers!
 

I have transferred through LHR T3 plenty of times but I now have a slightly different situation than all those other times. We are arriving on UA SFO - LHR and are continuing after a couple of hours on BMI. When you go through the transfers check-point, can you return to T3 or are you forced to go to whatever terminal BMI uses (I know it is not T3)? I want to stay in T3 for a while to take a shower and check out the new SK lounge. I know you have to go through the transfer place to do this but can I still stay in T3?

I have a similar question as a friend and I are arriving on differnt flights. I would love to be able to meet him at the gate.

No. For a bmi connection you will almost certainly be put on a bus over to Terminal 1 as soon as you reach the Flight Connections Area. The airport operator, BAA, is very inflexible about this and, due to the nightmares of transferring at LHR generally, mandates that no passenger can be in the gate area of a terminal unless they are departing on a flight from that terminal. Exceptions have been known but are relatively rare (the staff involved are breaking the rules (and arguably UK law) and can find themselves in trouble).

The only way to meet a friend would be to delay going to the Flight Connections area and hanging around the gate areas in T3 until your friend's flight arrives. Unfortunately there are no Arrivals information screens in the gate areas, so you would have to ask airline staff (who may decide to frog-march you straight to the Connections Centre!).

Well, I think you might have a chance. Your first obstacle is the guy who checks the BP at the T3 connections security. I was in the position of only having a paper ticket a few weeks ago and need to check with SK transit check-in. The guy casually stamped the back of one of the coupons. I don't think he bothered scrutinizing the ticket. If you get BD BPs on UA stock then I think you should be able to slip thru. I he is helpful and points out that BD is in T1 then tell him that you need to go to the UA transit desk to reroute your ticket to SK or something.

However, a nasty matron at a lounge might give you a hard time because you don't have a BP for a T3 departure -- if that's the regulation. But you have three at bats: UA, AC/SK and SQ.