Geneva

Geneva was a city in Switzerland where the international headquarters for UNIT (TV: Spearhead from Space, et. al.) and for the International Space Command were located (TV: The Tenth Planet). During the Brigadier's tenure with UNIT he consulted frequently by phone with Geneva. (TV: Spearhead from Space) The CIA's files on the Torchwood Institute had referrals going back to Geneva and above. (TV: The New World) During the Toclafane invasion, the population of Geneva was massacred. (TV: The Sound of Drums)

After turned humanity into "The Master Race", he consulted with a UNIT officer in Geneva. (TV: The End of Time)

Behind the Scenes
The location of UNIT's central headquarters in Geneva presumably was chosen because of the number of United Nations organisations centred there, and its cultural association as an internationally neutral location.