19. Lost Forever
https://www.youtube.com/watch?v=OgxByptlOGE While almost every episode of Doctor Who was copied for sale overseas before their destruction in the now legendary BBC archive purges, there is one exception. Because the BBC believed that nobody would watch television at Christmas (well give you a moment to laugh at that with nearly fifty years of hindsight behind you), Episode 7 of the twelve part story The Daleks Masterplan (titled "The Feast Of Steven" and scheduled to air on Christmas Day) was written as a standalone light-hearted episode that wouldnt disrupt the main story and ended with the Doctor breaking the fourth wall to wish the audience a merry Christmas. Because of this, it was the only episode not sold overseas before its destruction because it wasnt thought to be necessary. Thus it is the only episode that is almost definitely lost forever. However, the audio survives as with every other episode along with a number of stills, enabling some fans to create reconstructions of the episode.
18. The Whomobile Wasn't A Prop
https://www.youtube.com/watch?v=q3noPBEtOBk The Third Doctors flying car (known both as the Whomobile and the Alien) may have only made a few appearances before the Third Doctors Regeneration but its history away from the programme is markedly more interesting than its time onscreen. Relating back to his love of gadgets, the Whomobile was commissioned and owned by Jon Pertwee in the hopes that producer Barry Letts would approve of it and include it in one of his episodes. It was also a fully street legal vehicle with a top speed of 105mph rather than a prop, and was used by Pertwee for years after he left the programme to appear at charity events.