The Next Doctor

According to Neil Gaiman, the Cybus Industries Cybermen "zapped off into time and space" by the Doctor at the end of this episode eventually encountered the Mondas Cybermen; their "cross-breeding and interchange of technology" resulted in the variety of Cybermen seen in "Nightmare in Silver".[8]

A Cybershade on display at the Doctor Who Experience

Pre-broadcast publicity, based on excerpts from Davies' book Doctor Who: The Writer's Tale, revealed that the Doctor would meet a man played by David Morrissey who also claims to be the Doctor. In further excerpts, Davies commented, "The best title for this episode would be The Two Doctors... but maybe not. The New Doctor, perhaps? Or The Next Doctor? I quite like The Next Doctor."[9] The book also contained two pictures from a scene cut from the end of the previous episode, intended to segue into the special echoing the previous two series. This scene was included on the series boxset.

Following the success of the previous year's Christmas special, "Voyage of the Damned", which guest starred pop star Kylie Minogue as one-off companion Astrid Peth, Russell T Davies had initially felt tempted to copy this format with another high-profile guest star, but decided against it after jokingly offering up "Cheryl Cole on board the Hindenburg" as an example.[6]

Regarding an unanswered question (from a child) of why a gigantic robot in London 1851 "isn't in the history books", Davies and Gardner jokingly offer several possibilities ranging from there being alternate history of Doctor Who Britain, pointing out "a spaceship didn't fly into the Big Ben in 2006 either" (in the episode "Aliens of London") or that perhaps "maybe everyone was retconned by the soon-to-be-born Torchwood, or something."[7] A line in Steven Moffat's series 5 episode "Flesh and Stone" has the Doctor recall the CyberKing's rampage, attributing history's failure to record it to the cracks in time and space that are causing time to be unwritten.[10][11]

Davies, from a writer's standpoint, was also unhappy with the final scene in the episode where the Doctor gets rid of the CyberKing with the convenient Dalek dimension vault but during the writing process he couldn't think of another way to stop London being crushed by a giant robot. Later, after the episode was produced, a different idea came to him. In this alternate ending Davies imagines, Miss Hartigan "should have destroyed the Cybermen when she screamed... but she's still in the chair", as the CyberKing falls to the Earth, the Doctor calls out to her saying "Save them." This version would have Hartigan redeem herself as she is the one to cause the CyberKing to disappear, with no need for what Davies calls "a silly Dalek continuum dimension vault". Julie Gardner felt this would have been a superior, "marvelous" ending and Davies says he "can't bear that there could have been a better ending than we actually transmitted".[7]

Davies also feels he would like to write a BBC Books novel, set in the midst of that brief scene where Jackson Lake is in the Doctor's TARDIS in which the Doctor takes Jackson to another planet, ending with the "no no no" scene before Jackson invites the Doctor to spend Christmas dinner with him.[7]

Davies claims that he attempted to make Jackson Lake's companion Rosita a combination of Rose and Martha so that she felt like a companion before she had done anything.[12]

Filming for this episode was conducted in April 2008 at Gloucester Cathedral,[13] St Woolos Cemetery in Newport[14] and the streets of Gloucester, where shooting was hampered by up to 1,000 onlookers. The main setting of Torchwood, their Torchwood Hub was also redesigned and used as the workshop for the children.[7]

David Morrissey is the main guest star, playing "a character called The Doctor – a man who believes himself to be a Time Lord".[15] He was influenced in his performance by previous Doctor actors William Hartnell, Patrick Troughton and Tom Baker, as he believed there was "a truth" to their performances because they "never saw [Doctor Who] as a genre show or a children's show".[16] He is joined by Velile Tshabalala as Rosita, the companion to Morrissey's "Doctor", whom Russell T Davies describes as "probably cleverer than the two of them [the Doctors] put together". For Tshabalala, the character came naturally because her "feisty cockney girl" characterization was very "close to home" for her.[17]

Dervla Kirwan plays Mercy Hartigan, who Russell T Davies describes in the episode's podcast commentary as "dark a villain as you will ever have". A lot of her characterization goes unstated, but Russell discussed it in long conversations with Dervla Kirwan and fellow executive producer Julie Gardner. Davies characterizes Miss Hartigan as "a victim of abuse", for whom the subtext suggests a "terrible backstory" which is symptomatic of her being "part of [this] Victorian Age." Davies describes this as being "a powerless woman who's been in servitude or far worse all her life", but holds his tongue from saying her precise profession, relaying: "I'm talking quite discreetly around this because there are children listening and watching and there's only so far I should go." He does however explain that "She's had terrible things done to her" which is responsible for her "really twisted character where she sexualizes everything." In terms of costume, "she wears red" because "everything's inflammatory with her". "And in the end, actually" Davies discusses how to escape her male oppression she "becomes a man, she becomes the CyberKing. She has to go through this extraordinary process because she's so damaged."[7] Kirwan would later go on to voice Miss Quill, replacing the original actress Katherine Kelly, in the audio dramas of the spin-off Class produced by Big Finish Productions in 2019.

Millennium FX's Neil Gorton's original design for the Cybershade took the existing Cyberman design and "refurbished" it by adding rivets and a copper finish. The design was cost-effective but Russell T Davies did not believe it was the right approach. He sketched a new design for the Cybershade that was "a crude version of a Cyberman, all angular and blocky, with its trademark handlebars set at a jaunty angle and shrouded in flowing black robes". Gorton used Davies' sketch to create a fiberglass mask that the Cybershade actors wore over their heads. Costume designer Louise Page made the flowing robes, that were "light enough to not restrict movement" to complete the Cybershade costume.[18] A new head design for the Cyber Leader was also introduced, sporting a black face and handles and an exposed brain similar to the one of the Cyber Controller from "The Age of Steel" (2006).

Originally, Gardner relayed that there was a widespread dissatisfaction with Hartigan's CyberKing crown. The original helmet, he remarked "was like the Cyberwoman's head from Torchwood" (referring to the episode "Cyberwoman"), literally "a Cyberman's head on Dervla Kirwan" or "as if Dervla Kirwan decided to go to a [fancy dress] party as a Cyberman." Davies' response was "Oh my lord, no." The production team however worked hard, and in two days produced the final headpiece seen in the episode which Davies described as "beautiful", because it's "Victorian and it fits the design." In the scene after the headpiece is placed on her, Dervla wore black contact lenses and SFX company The Mill helped to get rid of "any traces of white" in post-production.[7]

Unfinished cover art of The Next Doctor DVD. This version lacked the hot air balloon in the top right corner, which was considered a spoiler by the production team and so a balloon-free version of the cover was released to the web prior to broadcast. The final version of the cover includes the balloon.

The DVD was released in the United Kingdom on 19 January 2009.[24] The DVD features a full set of end credits newly produced in a "cinematic" format to replace the broadcast version. There is an hour of special features on the disc, including the full Doctor Who Confidential for the episode, a cut-down edition of the Doctor Who Prom hosted by Freema Agyeman and the seven-minute mini-episode "Music of the Spheres".[25] The DVD was re-released on 11 January 2010 in the boxset 'The Complete Specials', packaged with the remainder of the 2008–10 specials.

The ten Christmas specials between "The Christmas Invasion" and "Last Christmas" inclusive were released in a boxset titled Doctor Who – The 10 Christmas Specials on 19 October 2015.[26]

Although "The Next Doctor" was not filmed in High Definition, it was up-scaled for Blu-ray, with DTS HD 5.1 Audio, and released as part of the 2008–2010 Specials boxset, for Blu-ray, entitled "Doctor Who: The Complete Specials".[27]