Prisoner (The Mind of Evil)

A prisoner was an inmate of Stangmoor prison. When Harry Mailer and led a breakout, he kept guard over the main gate.

When Brigadier Lethbridge-Stewart (posing as a lorry driver) arrived at the prison to drop off some food, the prisoner allowed him to go in unaware that inside the Brigadier's van was a UNIT assault team. The prisoner was then knocked out by one of the UNIT soldiers. (TV: The Mind of Evil)