It is a fantastic place.....I visited in June this year and wrote an article about it....here is an extract.
The Last part of the tour for me was indeed the most impressive, visual control, call-sign 'Heathrow Tower'. This is a small gallery at the top of the building. Here ATCOs control the departures, arrivals, ground traffic and even the airfield lighting. This is a seriously busy place and this was apparently a quite day. It is impressive to see a control (or whatever the collective noun for ATCOS is) of professional ATCOs at work. Methodical, cool and in control. At 3pm, the daily runway switch played out in front of us. Every day the departure traffic and the arrivals traffic swap parallel runways to provide better noise abatement. As a large ballet played out over hundreds of acres of land, it was the climax to an excellent day.