The episode is a crossover between Doctor Who and its spin-off series Torchwood (2006) and The Sarah Jane Adventures (2007). Writer Russell T. Davies described the crossover by saying "it's simply doing what kids do in their imaginations ... they would think nothing of having their Dalek toys battling Star Wars droids. Why not have all the factions of the Doctor Who universe going into battle together?".
Russell T. Davies had been impressed with Russell Tovey's performance as Alonso Frame in Voyage of the Damned (2007) and wanted to include him in the story. He would appear when the Doctor and Donna travelled to the Shadow Proclamation, and assist them in dealing with his superiors there. He would then journey with them in the TARDIS to the Dalek Crucible, only to be exterminated, allowing Davies to sacrifice somebody recognisable without having to kill off one of the show's better-established characters. This had been a concern for Davies during his development of the narrative, because he felt that the death of one of the Doctor's allies was necessary to demonstrate the scale of the adventure. This was scrapped when Tovey became unavailable.
The scene in the Shadow Proclamation was originally planned to show many more aliens old and new including: Sycorax, Hath, Vespiforms, Krillitane, Gelth, Cybermen, Isolus, Graske, Hoix and even a giant adult Adipose. This was axed because it would have used up half the episode's allotted budget in about 30 seconds.
The most cast names (6) to appear in the opening credits of Doctor Who