According to writer Anthony Horowitz, the real American company that was guilty of cooperating with the Nazis was Standard Oil although he chose to change the name to Global Oil.
IG Farben, the company guilty of war crimes in their use of Auschwitz slave labor was the name of the company that did these atrocities. Monowitz was leveled after the War, so according to Horowitz what appears in the episode was constructed by ITV. Farben is still in business today, as is Japan's Mitsubishi.
One of the characters says a line to the melody of the children's song. "The Hokey Pokey." The song was written in Britain in 1942 as "The Hokey Cokey" or "The Hokey Pokey" and emerged in the United States in 1946.
The location for the external shots of the MI5 HQ is the old Port of Liverpool building on Canada Boulevard at the Liverpool waterfront.