10 Times Doctor Who Broke Its Own Canon

In The Christmas Invasion, soon-to-be former Prime Minister Harriet Jones refutes allegations that the Guinevere One probe – which was sent into space to explore Mars – is a waste of money, telling the cynical journalists that:

"The Guinevere One space probe represents this country's limitless ambition. British workmanship sailing up there among the stars."

The implication here is that the British space programme is something relatively new, and that Guinevere One provides the UK's first opportunity to land on Mars.

But wait, doesn't anyone care about history?!

Britain had already landed a probe on Mars decades prior to The Christmas Invasion, in the Third Doctor serial The Ambassadors of Death. This probe was called Mars Probe 7, and unlike Guinevere One, it was manned! However, Earth lost contact with the astronauts, who had been captured by aliens. The Doctor then piloted a recovery craft to locate the astronauts and secure their release.

The events of The Ambassadors of Death are completely ignored by The Christmas Invasion, and what's more, they're directly contradicted in The Waters of Mars, which states that the crew of the Bowie Base One are the very first humans on Mars.

It's possible that UNIT covered up the whole Mars Probe 7 affair, but then again, there was a journalist present throughout the recovery mission, broadcasting live on TV!