Continuity mistake: When Daniel Llewellyn meets Harriet Jones, she pulls out her ID card when she introduces herself. The scene cuts to a shot of Llewellyn saying that he knows who she is, and when it cuts back to Harriet, the ID card has vanished without her making any movement to put it away. (00:16:10)
Continuity mistake: When the TARDIS crash-lands at the beginning, it comes to a halt in a corner of the Powell Estate's courtyard, by the garbage containers. Later, when Rose is watching through the window as blood-controlled people walk through the courtyard, the TARDIS has moved further out into the plaza. (00:23:05)
Continuity mistake: After the Sycorax ship has arrived above London, when Rose has decided that they need to shelter in the TARDIS and is explaining this while preparing to put a housecoat/dressing gown/bathrobe on the unconscious Doctor, the garment jumps between the bed and her hands in a few shots. (00:30:25)
Continuity mistake: After the Doctor's challenged the Sycorax leader to a swordfight, when he's asking about the rules of combat while taking his dressing gown (bathrobe) off, he starts taking it off beginning with his left arm in two successive shots. (00:43:58)
Factual error: When the Doctor regrows his hand during the swordfight, he says that he can do this because he's still within the first 15 hours of his regeneration cycle, and there's still residual energy in his body. However: In both this scene, and the episode's opening scene, when the TARDIS arrives in London, it is full daylight. The episode takes place on Christmas Eve and Christmas Day, 3-4 days after the Winter Solstice. London, at 51°N latitude, has a night longer than 15 hours at that time of year, meaning the Doctor should have been out of luck.
Continuity mistake: When Cassandra reveals her presence to the Doctor, she starts off by turning him to face her, then pulling his tie out of his jacket with her right hand and tightening the knot with her left hand, in a shot facing him. In the next shot, facing her, she has her right hand holding the knot of the tie. Finally, just before Cassandra reveals her identity to the Doctor, shortly later, which hand is holding the tie changes again. (00:23:20)
Continuity mistake: When Cassandra, possessing Rose, confronts the Doctor after he wakes up in one of the clone pods and tells him how she intends to kill him, her hand changes position between the shot from inside the pod, when she rests her hand on the front, and the next shot from outside the pod. (00:24:20)
Continuity mistake: When Rose gets into one of the hospital's elevators early in the episode, stock footage of an elevator descending is shown. When the Doctor, Rose and Cassandra (possessing her) go into an elevator shaft later on, it looks and is shaped completely differently. (00:34:05)