Deliberate mistake: The final Auton attack in this episode is supposed to take place in a busy London street, but it is a pedestrianised area, and several shots reveal this. For example, there are no road markings visible, no apparent distinction between pavement and road, and a bus stop appears to sit in the middle of the 'road'.
Revealing mistake: When Mickey closes the wheelie bin lid, he then finds the plastic stuck to his hands, he lifts his hands up and the plastic stretches like tar. If you look closely when he lifts his hands up for the first time, you'll see that a shadow of one of his hands is cast on his shirt, yet there is no shadow of the strands of plastic stuck to his fingers.
Factual error: In the opening shot of this episode, we see the Earth from space. The camera then zooms into Western Europe, the UK, London, then into Rose Tyler's flat, where a jump cut to an alarm clock shows its 7:30am. But look again at the start of that sequence: it shows that it's daylight over the UK - and over the USA. This is of course impossible. When it is 7:30am in London, it is 2:30am in New York, as Eastern Time is 5 hours behind UK time. Usually, in New York, at 2:30am it is not daylight because it is the middle of the night.
Continuity mistake: When the three bride Autons attack Jackie, and they open their hands one at a time, it is clear that when the second Auton opens its hand, all three are already open. After it cuts to Rose, and back to Jackie again, the third one opens (even though we just saw it already open).
Revealing mistake: The Doctor and Rose locate the "metal" hatch that leads down into the "Plastic's Leader" blob. Watch carefully after the Doctor removes the "metal" hatch and moves it aside. The entire hatch "pops-up" a second later. This is because it is plastic and it was suctioned to the floor.