Sergeant (The Five Doctors)

A sergeant was on Colonel Charles Crichton's UNIT staff at the time of the Brigadier's post-retirement reunion.

When the Second Doctor arrived at Colonel Chrichton's office to visit the Brigadier, the Sergeant told him he was not allowed in Crichton's office. Replying that he was allowed everywhere, the Doctor entered the office anyway. The Sergeant reached out to stop him but only succeeded in removing his coat. Crichton dismissed him once he determined that the Brigadier knew the Doctor. (TV: The Five Doctors)

Behind the scenes
This sergeant was originally meant to be Benton, but John Levene declined because in the script he would have to not recognise the Second Doctor. Levene thought that Benton would have remembered that version of the Doctor and not made such a mistake. (DWM 230)