When the Second Doctor arrived at Colonel Crichton'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 the Doctor but only succeeded in removing his fur coat.
Crichton dismissed the sergeant once he determined that the Brigadier knew the Doctor. (TV: The Five Doctors)
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)