As a spotter in the late 50s, living near LAP, I spent many hours in and on the Queen's Building. There was a cartoon cinema in the lobby, believe it or not, and on the roof was a commentary box, manned by a short fellow who sounded like a woman on the PA.
In bad weather we would camp out in the cafeteria, and order just enough tea and biscuits to avoid being slung out. We had a superb view of all Westbound approaches, and of the apron.
I was airside at LHR a couple of years ago watching inbound baggage handling, and when I looked up I was stunned to see the well-remembered outward-sloping windows of the old cafeteria. Nowadays they just look out on the shed roofs.