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T1 is due for demolition once T2 opens, I believe T2 is going to have the ability to handle domestic where as T3 does not have that facility, hence the connection from T1 to T3. Is T4 capable of domestic and international ?"
AFAIK, plse correct if it is wrong: (1) VS domestic will be in LHR-1 where there is an underused domestic pier; (2) when LHR-1 is demolished this will shift to LHR-2 where there will be a domestic arrivals area (as in LHR-5); (3) VS will move its entire LHR operation to LHR-2 taking the space originally earmarked for BD.
LHR-1 to LHR-3 is an easy transfer, whether on the airside bus or landslide via the tunnels that link the terminals and the bus/rail/tube stations.
Will BA move its LHR-1 operation to LHR-2 as well?
LHR-3 and LHR-4 do not have domestic arrival areas.