Thames House
From Tardis Wiki, the free Doctor Who reference
Thames House was the headquarters of MI5, located in London.
When the 456 returned to Earth, a special tank was built to house their ambassador on the thirteenth floor. (TW: Children of Earth: Day Two) Prior to their arrival, all the children of the Earth pointed in the direction of Thames House. (TW: Children of Earth: Day Three)
Jack Harkness and Ianto Jones confronted the 456 Ambassador at Thames House. The 456 released a virus which killed everyone the building, except Dekker who survived by wearing a hazard suit. (TW: Children of Earth: Day Four)
