ATMOS factory

The ATMOS factory was located in the London area. It was secretly run by the Sontarans, who operated a cloning tank in the facility and replaced Martha with a Clone to infiltrate UNIT. (As Donna Noble noted, none seem to get ever get sick or go on leave) During the Sontaran invasion of Earth, it was the site of a battle between Sontarans troops and UNIT. (TV: The Sontaran Stratagem/The Poison Sky)