Boris Johnson

In the aftermath of the 5 March 2005 Nestene invasion of Earth, an incapacitated human body was found by a decaying Auton which housed the remains of the Nestene Consciousness. By merging with the human, the Auton formed a new, stable Auton, successfully preserving the Nestene Consciousness. The human had blond hair. (PROSE: Revenge of the Nestene) According to Box, a "plastic duplicate" had become prime minister by 2019. (PROSE: Out of the Box)

Behind the scenes
Though the human is never named they are implied to be Boris Johnson, the Prime Minister at the time of the story's release. At the time the story was set Boris Johnson was an MP so likely would have been in Westminster.