Upstairs, Downstairs - Out of Costume - Before Upstairs, Downstairs 2

In 1967, Pauline Collins played Samantha Briggs in the Doctor Who story, The Faceless Ones. The character had originally been intended to be an regular companion of the Doctor, but Collins didn't want to commit herself to an on-going series at this time and so her character remained confined to this one story.
Of the five episodes of this six-part story that Collins appeared in, sadly only one episode still exists. Click on the above to see a larger version. (NB Pauline returns to Doctor Who playing Queen Victoria in the new 2006 season).
A couple of years later, in 1969, Collins appeared in The Liver Birds - a BBC sitcom about the life and loves of two single girls living in Liverpool, also starring Polly James. After making a pilot show and four subsequent episodes, the BBC abruptly curtailed the series and Collins departed under something of a cloud.
The reasons given for Collins' vanishing act vary - a "clash of personalities" between the two leads being the most common explanation.
A year or so later the programme was re-launched with Nerys Hughes instead of Collins, and then ran successfully for over 80 episodes, including a 1996 revival series. Subsequently, the Collins episodes were more or less written out of TV history, and relatively few people seem to be aware they were made. All five have been wiped, and only a few pre-filmed location scenes (and the title sequence) from the second episode still remain in the BBC archives.

An uncredited Gareth Hunt plays a bit part in Space: 1999. The episode is called Guardian Of Piri and was filmed in May 1974. Apparently, Hunt's role was to have been bigger, but he had an argument with the director, Charles Crichton, and walked off the set. His part was rejigged and given to Michael Culver.

Jean Marsh in, of all things, a 1959 episode of CBS' The Twilight Zone called The Lonely. In the story, Jack Warden plays a lonely criminal imprisoned on an asteroid. A sympathetic supply-ship captain takes pity on him and leaves him a robot friend, with whom he falls in love! Marsh remembers: "I remember filming The Twilight Zone out in the desert and I’ve never forgotten the address of the place where I was staying - Furnace Creek Inn, Funeral Range, Desolation Canyon, Death Valley. Out there every place had been the scene of some pioneering disaster. It was 130 degrees in the shade. I had an air-conditioned caravan, sacks of ice, jugs full of pure lemon juice, sticks of iced cologne, cool clothes, a swimming-pool and a nurse standing by - and I still felt dodgy from time to time! The crew, on the other hand, were falling about all over the place." Click the picture for a bigger version.