Streaming for those in the US
http://www.shoutfactorytv.com/series/sapphire-and-steel
First 4 seasons available, but I believe it's USA only.
Honestly, I had never heard of this show before. Decided to watch the first episode because I recognized David McCallum, or Ducky from NCIS. Always wanted to watch his earlier stuff but never got around to it.
Seems interesting, will be watching the rest soon.
~Currently binge watching: Kaizoku Sentai Gokaiger & Sapphire & Steel~