ATMOS factory

The ATMOS factory, located in the London area, was secretly run by the Sontarans, who operated a cloning tank in the facility and replaced most, if all not, of its personnel with clones of the original workers. (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. (DW: The Sontaran Stratagem/The Poison Sky)