Wasn't the West London Terminal on the Cromwell Road (now a Sainsburys) actually a BEA operation. You could check in there and get bussed over to LHR (T1).

BOAC would have been in the old Imperial Airways Building by Victoria Station which is now occupied by the NAO. There is/was still quite a bit of Art Deco airline architectual features on the building.

Pan Am used to have an office just around the corner not far from where Casa Pupo used to be.

I'm not sure/don't recall BOAC offering an in-town check-in service. I do remember them having a massive town office at the bottom of Regents Street by Air Street (Piccadilly end) where you could get innoculations. Alternatively, you could get innoculations on arrival at various places when your mother had forgotten to bring along your innoculation certificates!! Bahrain wouldn't let you in without your Cholera TAB certs.

And yes, I do remember flying long haul, multiple sectors without IFE. I stll take along a good book like the old days just in case the IFE goes on the fritz.