I did an Air Britain visit to Southern Air Traffic Control Centre in about 1966 when there were still radar heads just outside the building and 'procedural' and FIR were still there. By the time I was summoned to West Drayton about 3 years later, the procedural side and FIR had moved there leaving just radar at Heathrow.
All the time I worked at the Heathrow Radar section of LATCC I never knew there was a bunker underneath. Heathrow Mil, forerunner on LonMil, operated above ground mostly in a separate room but they did occasionally operate from a couple of 'fonts' in the civil radar room under the guise of 'SEJAO', which eventually became LJAO.
The man who recorded VOLMET also operated at the old radar unit. One of my colleagues incurred his wrath one morning when he accidentally beeped his car horn; a VOLMET update was just being done and the 'beep' went on the tape, so he had to start again! Apparently the window flew open and a stream of profanities was directed at my colleague!