Steven Berkoff proved difficult to work with. He repeatedly went against the wishes of Douglas Mackinnon, in some cases just plain refusing to do what he was told, deliberately ruined takes (sometimes by reading his lines as badly as possible), and had several temper tantrums. Virtually all the footage they shot featuring Berkoff was unusable, and the ending as broadcast is all they could cobble together from the few scraps they were able to salvage, plus some pick-ups filmed later on with just Karen Gillan and Arthur Darvill (as well as some shots of Berkoff which were allegedly taken from when the camera was left running between takes, because even the filmed footage of Berkoff walking across the floor could not be used) - it was not originally the intention for Shakri to be a hologram, or for the plot to effectively be resolved entirely by the sonic screwdriver, but that was all they were able to do with what they had.
Kate Stewart mentions having "ravens of death" in the Tower. There are six captive ravens that are cared for and live in the real Tower of London. Legend has it that these ravens are the guardians of the Crown and the Tower, and if the ravens ever go away the kingdom will fall.
Matt Smith put disgust into The Doctor's remark concerning Twitter, reflecting his real-life decision to stay off the social network.
The episode was largely restructured to introduce the invasion storyline earlier. The episode originally began with scenes such as the adventure with Henry VIII and Amy at the engagement party.
The climax was originally very different. The Shakri was physically present, rather than merely appearing as a hologram. He was defeated when Amy and Rory attacked him with the syringes they had retrieved from the orderlies, and the Doctor used his sonic screwdriver on the Shakri's devastating ocular weaponry. However, it was felt that this part of the narrative detracted from the focus on Amy and Rory's life together, and so Chris Chibnall prepared new material to replace it. As a result, new material in the Ponds' house was shot.