Alternative 3 (and Capricorn One)
What I remember was a brilliantly executed UK TV programme called "Alternative 3". Billed as a "documentary" it followed a story about scientists involved in the Mars mission going missing and ended with a "classified" film clip that showed something scuttling under the Martian surface when Viking landed.
I was 11 at the time, so thought it was real ....
And the fact and fiction loosely danced in "CapricornOne"