Trading Post

 was a British special effects firm steadily active from roughly 1962 to 1969. It appears to have been run by two relatives, Bill King and Malcolm King. They were usually, but not always, mentioned during the Patrick Troughton era whenever Bill King was credited for special or visual effects design. In all, they appear on the credits of three season 6 serials: The Invasion, The Krotons, and The Seeds of Death.