FROM WHAT I CAN REMEMBER THE LUGGAGE WAS CARRIED IN TRAILERS TOWED BEHIND THE BUS
The original BEA buses were as shown near the bottom
Google Image Result for http://www.countrybus.org.uk/rf/RF50/366zBEA.jpg
THe baggage was carried at the rear.
The later BEA buses were Routemasters with a special dispensation to have a trailer.
Airport Buses
The BEA buses ran from WLAT ( West London Air Terminal) in the Cromwell Road ( Now a Sainsbury's store) but the vehicle ramps are still there.
Check in was upstairs and boarding was down the stairs to the appropriate gate where the bus was boarded.
BOAC buses ran from The Victoria Air Terminal by Victoria railway station.