BBC Film and Videotape Library
From Tardis Wiki, the free Doctor Who reference
More commonly known as the BBC Archives, the BBC Film and Videotape Library was an entity created in the late 1970s in response to the realization that a large amount of early television material was now missing. Doctor Who was just one of many series to have episodes missing from the BBC, others including Dad's Army and Out of the Unknown.
An early omission from the run of Doctor Who episodes was The Feast of Steven, (Episode 7 of The Daleks' Master Plan which, while recorded on 405 videotape like every other William Hartnell episode, was erased a short time after being made and was not telerecorded like the other episodes of the series because, due to its seasonal nature, it did not fit well into continuity.
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