UNIT corporal (Invasion of the Dinosaurs)

UNIT Corporal was the head of UNIT solders, left behind in an evacuated London to track time-displaced dinosaurs. (DW: Invasion of the Dinosaurs)

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