There is more information regarding the dispersal of the Ops room of Northolt on p243 of "The Battle of Britain, Then and Now" (1980 edition, published by After The Battle), with photographs of the buildings in question. These are a small shop in Ruislip manor and a large country house, Eastcote Place.
As I type this, I'm looking at Eastcote Place through my window. Apart from the dispersal of the Ops room, Eastcote Place was also requisitioned for use during the preparations for D-Day. It is mentioned in Lawrence Wright's book "The Wooden Sword", the story of the Glider Pilot Regiment during WW2. He was an architect and member of the London Gliding Club, who was impressed into service at the beginning of the war to help set up the GP Regiment. He helped produce a model of the landing zone at Pegasus Bridge for briefing the glider pilots. Behind me is the site of RAF Pembroke Park, which was one of the outstations of Bletchley Park, where were sited a number of the Bombes used for decoding the Enigma messages. After the war it became the first site of GCHQ, before it moved to Cheltenham. The site is currently being redeveloped as a housing estate.