Theory:Doctor Who television discontinuity and plot holes/The Christmas Invasion


 * Early in this episode, a Routemaster bus briefly appears. However, Routemasters were actually removed from active service on 9 December 2005.
 * It could have been a heritage service, and maybe routemasters being replaced weren't the main concern in this time-frame, especially when Earth has just had to cover up events such as the Slitheen encounter.


 * It is left unexplained why Britain's space program has apparently reverted to celebrating unmanned probes arriving at Mars when The Ambassadors of Death established that by this time Britain had already sent manned missions to Mars.
 * There is actually a real-world example of such reversion occurring: America's NASA program sent manned missions to the Moon in the 1960s and 70s yet by the 2000s had reverted to again sending unmanned probes to the moon. The secrecy involving restricting public knowledge of alien life (depicted in this episode and many others pre-The Stolen Earth) might also imply that those earlier missions may not have been public knowledge.


 * After indicating to Rose how important Harriet Jones becomes to Britain and planet earth (DW: World War Three), here he proceeds to sabotage her career. What about his many spiels about his being forbidden to change history?
 * Some events can be changed, as established in The Fires of Pompeii. This must be one of them. In any case, Harriet Jones was to be vital to the world in The Stolen Earth. In that story, her death was not witnessed by the audience or any of the characters. It remains possible then, that she survived and did eventually serve the two more terms and usher in Britain's Golden Age, as predicted by the Ninth Doctor. Alternatively, it was the Doctor deposing Harriet that led to the Master to be elected in her place.


 * How is the scarf that the Fourth Doctor wore in the Tardis wardrobe? The Fifth Doctor took it apart in his first episode.
 * Over the interim years (perhaps centuries) the Doctor could have acquired a new scarf, or simply resewn the old one.
 * It could have been a wholly different one. In the movie, when the Eighth Doctor is searching the hospital for clothes, the first thing he stumbles upon is a scarf like the Fourth Doctor's, which he throws away.