Betts (The Green Death)

Betts was a UNIT soldier serving under Brigadier Lethbridge-Stewart. He was part of the convoy sent to Llanfairfach to destroy the Giant Maggots. (TV: The Green Death)

Behind the scenes
David Billa also played UNIT soldiers in The Three Doctors and Invasion of the Dinosaurs. It is unclear whether these are meant to be the same characters.