Soldier (Planet of the Spiders)

The Soldier was a UNIT soldier and technical officer that served under Brigadier Lethbridge-Stewart. While conducting maintenance upon the Doctor's new vehicle in UNIT HQ's carpark, he was approached by Lupton. He questioned the soldier upon the whereabouts of the Doctor. After an initial misunderstanding concerning the base's medical officer, he informed the man that the Doctor would be in his laboratory at this time of day. Having cleared that up, the Soldier requested a security pass from Lupton. At this point, Lupton attacked him with his advanced psychic powers and he was left for dead in the carpark. (DW: Planet of the Spiders)

Behind the Scenes
The Soldier was played by Pat Gorman, who played a UNIT Soldier in The Three Doctors (uncredited) and a UNIT Corporal in Invasion of the Dinosaurs. It is not unreasonable to assume that these three characters are one and the same.