Queens Building was the original central area terminal, but I don't think it was ever called Terminal 2; T1 was built to the north of it then T2 to the south, then QB became airline offices, crew reporting and flight clearance/AIS etc. There is a film occasionally shown on TV called 'Out of the Clouds' (starring the formidable James Robertson Justice as the captain of a BOAC Stratocruiser) which I believe depicts the interior of QB.
The original pedestrian tunnel which we used to walk through was the one now used for cars/taxis to the east of the 'main' tunnels.
S'land, you appear to be about the same age as me; I went to Chesham Tech from '60 to '67.