In the Third Doctor story The Ambassadors of Death, set around the 1970s, the British space programme successfully launches a manned flight to Mars. I believe there are references to British astronauts travelling quite far out in space in the Fourth Doctor serial The Android Invasion, set a couple of years later. But in The Christmas Invasion, which takes place in the early 2000s, isn't the Guinevere 1 probe referred to as Britain's first trip to Mars? It's been a while since I last saw it, mind you. Should we just regard this as a minor error on the writers' part?