On his return from RAF service in the early sixties, Mitton embarked on a career in children's television. He began working as a special effects technician on a series of programmes created by Gerry Anderson's AP Films that used a puppet technology called supermarionation. Mitton was a member of the supervising visual effects director Derek Meddings team, displaying a special skill in setting up the electronics necessary to blow up buildings on cue in "Thunderbirds" (1965–1966), "Captain Scarlet and the Mysterons" (1967–1968), "Joe 90" (1968), "The Secret Service" (1969) and "UFO" (1970–1971).