Despite fonky sets, insane costumes, purple hair and plot holes, I'm finding UFO at least as much fun now as when I watched it in reruns as a child. The willingness of the Andersons to let the plot take some very dark turns make it unlike most televised SF (Star Trek and the count-on-it 15-minute Happy Ending spring to mind) and compensate for the somewhat greater degree of pulpiness. (You can find most episodes on YouTube.)
In a wider sense ;), consider that both UFO and the earlier The Invaders are obviously disinformation, black propaganda tending to discredit any leaks about the Hidden Frontier as detailed in my writings at I Work On A Starship. C'mon, look at the obvious parallels: bell-shaped "flying saucers" landing onesie-twosie in isolated locations, humanoid-looking aliens (or humans taken over by aliens), opposed by a lone man everyone thinks is nuts (The Invaders) or a covert organization (UFO, obviously a reference to the USSF-NATO alliance then waging a war of feint and standoff with the Edgers' "Federation of Concerned Spacemen"). UFO in particular all but hangs a lantern on it by hiding SHADO HQ under a film studio! Anyone trying to reveal the real facts after those shows had been on the air would have been laughed at.
2 weeks ago