What's fingermen headquarter?

To be honest, i saw fingerman guarding New Scotland Yard building. In book 1 chapter 4. Then there was Derek Almond speaking with Roger Dascombe. Then there's Peter Creedy talking with Dominic Stone in book 3 and there were brief scene in book 2 chapter 14 well after it it has 15 floors building, and when Alistair Harper were talking with Creedy and Helen Hayer they were around one large building