Retrograde

On Frontios, a Retrograde or Ret was a person who had decided to leave the society and technology of the formal colony — as led by Plantagenet — in order to try their luck in the wilderness. At the time the Fifth Doctor, Turlough and Tegan visited, it was increasingly common for colonists to become Rets. To stem the tide, Brazen, with Plantagenet's assent, decided to simply have Rets shot as deserters. This policy, however, didn't seem to curb the Retrograde "movement". (TV: Frontios)