Originally posted by honey lamb
[If your originating flight arrives in T3 then [url=http://www.heathrowairport.com/portal/controller/dispatcher.jsp?CiID=2b66488779273110VgnVCM10000036821c0a____&ChID=217fbf54776d4110VgnVCM10000036821c0a____&Ct=B2C_CT_GENERAL&CtID=448c6a4c7f1b0010VgnVCM200000357e120a____&Ch=Flight+Connections&ChPath=Heathrow%5EGbl%5EHeathrow%5EGeneral%5EAirport+information%5EFlight+Connections&ChIDPath=9a485109350d3110VgnVCM10000036821c0a____^d7b3b727436d4110VgnVCM10000036821c0a____^e734b727436d4110VgnVCM10000036821c0a____^7544b727436d4110VgnVCM10000036821c0a____^8454b727436d4110VgnVCM10000036821c0a____^217fbf54776d4110VgnVCM10000036821c0a____]this[/url] is the way to go. You won't have to go on a bus - that is only for inter-terminal transit but to be honest I don't know which way it pans out in T3. I probably would have gone through customs and Arrivals and walked over to the ordinary check-in
You've saved yourself a good part of the bother by through checking your luggage. Beyond that, it's anyone's guess as to what the best strategy would be. IIRC, transfers within Terminal 3 happen on the right as you approach the immigration area, usually a line is formed near where the transfers to other terminals are managed (the latter get the bus treatment). Sometimes, the line for inter T3 transfers has been brutal, usually when busloads of US flights have arrived with a lot of folks transferring onto middle east/India flights. In which case HL's option of just walking through to regular T3 check-in would be the way to go. If you were transferring onto a Virgin UC flight, I'd guarantee HL's option would be far quicker with any kind of line at T3 transfer security, and not too much in the way of immigration crowds.
It's the same in T1, I've done the T3-to-T1 transfer, gotten on a bus, arrived at the connection center security line near the T1 passport control, which happened to be empty, while the line to get through security into the old T1/T2 connections centre was brutal. No brainer especially if you had been holding a BA Club boarding pass from T1.