UNIT soldier (The Ambassadors of Death)

An unnamed soldier was a member of the UNIT security detachment to the British Space Centre. He served as a guard at the complex' main gate. He was attacked and apparently killed by one of the aliens who was trying to break into the British Space Centre. (TV: The Ambassadors of Death)

Behind the scenes
The UNIT soldier was played by Max Faulkner, who later played Corporal Adams in The Android Invasion. They are unlikely to be the same character, however, since Faulkner's Ambassadors character doesn't make it out of episode four alive.