Since 1963, there have been over 800 episodes of Doctor Who. Although many of these are available to buy and watch on DVD, or via online streaming, there are 97 episodes which now only survive as audio soundtracks.
In the 1960s and 70s, programmes were rarely broadcast more than once, and there wasn't an option to buy them for viewing at home. As a result, the taps of old shows sat gathering diet - and taking up space - on the shelf, stored on expensive tape.
As a result, many programmes were 'wiped', either allowing the tape to be recorded on again, or simply 'junked' to get rid of them. This wasn't a practice confined to Doctor Who, or even the BBC, though the Time Lords travels are perhaps the most high profile case of 'missing episodes'.
Since the late 1970s, when the majority of junkings were stopped, numerous episodes of Doctor Who have been found and returned to the archives. Here's just some of the places that they've turned up...
7. Foreign TV Stations
6. ...but not always the ones who should have had them
5. A landfill
4. A School Fete
3. The basement of a church
2. In an abandoned BBC building
1. The BBC's own archive...
There could be more to find!
Between 1978 and now, 42 episodes of Doctor Who have been returned to the archives, but there's still another 97 which could be out there somewhere, just waiting to be discovered.
Doctor Who isn't the only classic television programme affected by the junkings, either, with episodes of Adam Adamant Lives!, The Avengers, Dad's Army, and a whole host of other programmes also missing chunks of their back-catalogue. Indeed, in many ways, Doctor Who got off rather lightly - at least we can still listen to the 'lost' instalments!
So keep your eyes peeled! Check in the loft, and at vintage fairs, because you never know where the next missing episode may turn up...