In 1968, when I was nine, I watched a Doctor Who adventure called `The Web of Fear' in which the Doctor battled robotic Yeti in the London Underground. Four years later I visited London for the first time and as soon as I went down into the Underground the memories came flooding back. I wished there was some way I could watch the adventure again, but even then this was no longer possible. At that time the BBC just didn't repeat programmes like `Doctor Who' (partly, though not entirely, due to the agreement with the actors' union Equity, which for obvious reasons preferred that new shows be made) and so, believing that they would never be needed again, they began wiping the master copies of the video tapes on which they were recorded. By the time I stood on the Piccadilly Line platform at King's Cross, not a single master tape of either William Hartnell's or Patrick Troughton's adventures remained in the BBC library.
To be fair to the BBC, the tapes were bulky and expensive and it made sense to reuse them. They could not have imagined that within a decade video recording technology would have advanced to the point where home machines were practical, using a cassette which could hold an entire six-episode Doctor Who story.
So the question is not `Why did the BBC dispose of so many episodes?' but `If the tapes were wiped, how come so many still exist?' The answer, as Richard Molesworth explains, is because copies were made on 16mm film for sales overseas. Unfortunately the contracts with the foreign TV stations required them to return the films to the BBC when they had shown them the maximum number of times, or to destroy them and send certified evidence that they had done so. This book attempts to trace the fate of these film versions, and explains how many of them escaped destruction. It goes into great detail on how certain copies were passed between different countries, and where appropriate when they disappeared from the records.
Now and again the odd episode does reappear, whether discovered in someone's attic or in a storeroom in, say, New Zealand mislabelled as another programme entirely. So there is still a slim chance that more episodes might reappear. But as this book makes clear, the last find was back in 2004 so as time goes on it becomes more and more unlikely that there is still something out there waiting for somebody to come across it. However you can't prove a negative, so it will never be possible to declare that there is definitely nothing more to be found.
This book will tell you virtually nothing about the content of the episodes themselves (there are numerous story guides available for that). But it will explain how the shows were made, broadcast, and disposed of afterwards. An index would have helped, but even without one the book explains the BBC's policy towards its own programmes in the far-off days of the nineteen-sixties.