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 realisation that much early television material was 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 seventh episode of the epic twelve-part adventure The Daleks' Master Plan, "The Feast of Steven", broadcast on Christmas Day 1965. This was recorded and broadcast on 405 line black & white videotape like every other William Hartnell episode, but lost forever shortly after it was screened when the videotape was erased for reuse. "The Feast of Steven" was not telerecorded like the other episodes of the series because, given its seasonal nature, it was considered unsuitable for overseas screening (The Daleks' Master Plan was thus offered for sale overseas as an eleven-part story) and also did not fit well into continuity.