The UNIT soldier was played by Max Faulkner, who later portrayed Corporal Adams in The Android Invasion. They are unlikely to be the same character, however, since Faulkner's Ambassadors character doesn't clearly make it out of episode four alive. Faulkner is in episode six, but it appears to be a production error. He goes uncredited in part six, and the scene appears to have been edited in from work actually meant for episode four. The very clear narrative intent of part four is that he was killed by the ambassador. Indeed, INFO: The Ambassadors of Death says that the script does actually indicate the soldier died — but that the manner of death is very different than what Michael Ferguson shot.