BKS' administrative offices were in Seymour Mews, London until moved to Hounslow when BAS was set up. The ops center was in Building 224, Heathrow north side, conveniently close to the Vanguard Club! LBA and NCL had equal status as out stations.
Not only did the Trident never put in an appearance but neither did the Britannia either, I have been perilously close to the far threshold, particularly landing 15 with a wet surface in a 748 never mind a T1E.
The Paris service was done by the Ambassador until their retirement in '69 and then by Viscount, if memory serves it was to LBG until after my time there.
I arrived just after the original wooden passenger terminal had burnt down and an old WW II hangar had been rapidly adapted to serve. Our crew room was a shed tacked on to the side of the maintenance hangar who's floor blew up as soon as the crosswinds went above limits (frequently).
It was all great fun and a fantastic start in aviation for a 200hr cadet fresh from Training School. 23.5k hours and nearly 1/2 a century later I wish I could do it all over again.