It's Christmas Eve 1851, and the Doctor arrives in London to learn of murdered men and missing children. To his astonishment, these events are being investigated by another Doctor -- but one with no memory of past incarnations, and sporting a suspiciously conventional sonic screwdriver. This Doctor and his companion, Rosita, believe the Cybermen are active in London, while the Doctor suspects that his counterpart's forgotten past hides a terrible tragedy. But whatever the truth of the other man's identity, they must find a way to work together to stop both the Cybermen and their ally, the ruthless Miss Hartigan.

For four years after its return to production in 2004, Doctor Who had settled into a comfortable recording pattern. A Christmas special would be filmed during the summer, after which the thirteen-part regular season would go before the cameras over the subsequent eight months. However, things would change in 2008, following the completion of Season Thirty. Executive producers Russell T Davies and Julie Gardner had decided to wind down their involvement with Doctor Who, and David Tennant was also leaning towards giving up the role of the Tenth Doctor. Furthermore, Davies feared that the audience would become complacent if a new season of Doctor Who routinely showed up like clockwork every year.

By the middle of 2006, it had been agreed that there would be no full season in 2009. Instead, several specials would be made to wrap up the tenures of Davies, Gardner and Tennant, while a new production team prepared to take over with Season Thirty-One in 2010. This plan faced its first test on April 11th, 2007, when Davies was asked to remain on Doctor Who for a fifth season by Jane Tranter, the BBC's Controller of Fiction. He declined the offer, but the Controller of Programmes for BBC One, Peter Fincham, was very unhappy to lose one of his most successful programmes for most of a year. In late May, he explored the possibility of abandoning the specials and putting a new production team in place to ready Season Thirty-One for Spring 2009. However, it was ultimately decided to adhere to the original plan.

Russell T Davies decided that each special would pair the Doctor with a one-off companion figure

Around the same time, discussions were taking place with Billie Piper, who had played the Tenth Doctor's original companion, Rose Tyler, until Doomsday in 2006. It had always been intended that Piper would return to Doctor Who, and one possibility under consideration was for Rose to rejoin the Doctor during the run of specials. However, it was eventually agreed that Rose would feature prominently in the latter episodes of Season Thirty, which would then draw her story to a close. As such, Davies decided that each special would pair the Doctor with a one-off companion figure, in the manner of Astrid Peth from the 2007 Christmas adventure, Voyage Of The Damned.

Another motivation for the series of specials was that it would allow Tennant to pursue other professional opportunities, without giving up his role as the Doctor. Indeed, he soon agreed to star in productions of Hamlet and Love's Labour's Lost for the Royal Shakespeare Company, which would run during the second half of 2008. As a result, careful scheduling would be necessary in order to ensure that the recording dates for the specials didn't conflict with these commitments. In particular, the 2008 Christmas special would have to be filmed before Tennant started rehearsals for the RSC plays, which meant that this would have to take place immediately following the end of work on Season Thirty.

Consequently, Davies was already contemplating 2008's holiday narrative around the start of May 2007. He decided to include the Cybermen -- taking inspiration from the image of them striding through the snowbound Antarctic wastes in their very first story, 1966's The Tenth Planet -- but he considered placing them in an historical context. For a brief time during the summer, he pondered a completely different option: a fantastical adventure set in a world conjured by the imagination of Harry Potter author JK Rowling, who would appear as herself. Tennant disliked this notion, which he felt would veer too closely to self-parody, and Davies began developing the Cyberman idea more intently.

Having settled on Victorian London for his historical setting, Davies sought inspiration in the Christmas stories of the era. In need of a companion figure, he considered pairing the Doctor with a grown-up version of the title character of Hans Christen Andersen's 1845 short story Den Lille Pige med Svovlstikkerne. Known in English as The Little Match Girl, it told the sad tale of an urchin who froze to death one New Year's Eve after experiencing beautiful visions in the glow of her dwindling matchstick supply. But Davies was still having doubts about the entire narrative, especially since 2005's The Unquiet Dead had already been set on a Victorian Christmas Eve. He contemplated shifting the adventure to the court of King Henry VIII, but rejected this notion on the grounds that it would not feature enough recognisable yuletide traditions, most of which postdated the sixteenth century. He also mulled another completely new idea, about a hotel which became displaced in time. Entitled “A Midwinter's Tale”, it was eventually given to Phil Ford to develop for one of the other specials, but ultimately went unused.

Russell T Davies and Julie Gardner discussed the possibility of cancelling the 2008 Christmas special

Davies' confidence in his ideas for the Christmas special was not at all improved by the slow development of The Stolen Earth / Journey's End, the climactic episodes of Season Thirty. By December 10th, the situation looked so grim that Davies and Gardner discussed the possibility of cancelling the 2008 Christmas special altogether. Davies, however, was determined not to leave the BBC with a gaping hole in its festive schedule, especially given the damage it might do to Doctor Who's relationship with Jay Hunt, who had just been appointed as Fincham's successor. Fortunately, Gardner was able to secure the funds to push back the start of production on the Christmas special by one week, giving Davies a few more precious days to write.

During January 2008, Davies' ideas about the Christmas adventure began to coalesce, with the story's fulcrum becoming the introduction of a new character who would claim to be the Doctor. This would enable Davies to invert the “standalone companion” idea, with the real Doctor acting as the companion figure to the apparent impostor. It also justified the Victorian setting, since it would be plausible for someone from that era to dress and speak in a manner that suggested an archetypal Doctor. Davies devised new monsters called the Cybershades, envisaged as monstrous black forms with the head of a Cyberman, which would act as servants and agents in much the same way as the diminutive Cybermats which had first appeared in 1967's The Tomb Of The Cybermen. Unfortunately, Davies' progress on the adventure was further hampered by a bout of bronchitis at the end of February. As a result, he did not start work on the script until March 3rd.

Davies' initial impression was that the story's title should be “The Two Doctors”, but he did not want to encourage confusion with 1985's The Two Doctors. He considered “The New Doctor” before settling on The Next Doctor, although he briefly opted for “Court Of The CyberKing” instead. By the time Davies finished his first draft on March 17th, however, it was back to being called The Next Doctor. The Little Match Girl character had evolved into the “Other Doctor's” companion, whom Davies named Rosita -- a conscious echo of Rose, Martha and Donna, the Tenth Doctor's three main companions. The murdered reverend was called Aubrey Fairchild, a name Davies had previously used for the doomed British Prime Minister in a scene ultimately excised from The Stolen Earth, and also referenced in Gary Russell's 2008 Doctor Who novel Beautiful Chaos from BBC Books. The staircase duel with the Cyberman replaced a similar rooftop encounter with the Cybershades. A late change was the notion of the infostamp freeing Miss Hartigan's mind from the influence of the Cybermen. It was added to avoid giving the appearance that the Doctor effectively used the infostamp as a weapon to kill her.

The Next Doctor originally began with the Doctor pursuing the Cybermen to Victorian London

The Next Doctor originally began by reprising the planned cliffhanger ending to Journey's End. Here, after leaving Donna Noble with her mother and grandfather, the Doctor returned to the TARDIS control... where Cybermen suddenly loomed up behind him. The Christmas special would begin with the Cybermen vanishing; the Doctor realised that they were falling through time, and pursued them to Victorian London. However, Doctor Who Magazine contributor Benjamin Cook suggested that the cliffhanger felt inappropriate, coming on the heels of Donna's bittersweet exit from the TARDIS. Although he was initially resistant, Davies eventually came to agree. Particularly persuasive was the fact that, unlike in past years, footage from the Christmas special would already be recorded by the time Journey's End was broadcast, which meant that a full trailer for The Next Doctor could be transmitted instead. A new scene was recorded to serve as the Season Thirty capstone, and Davies rewrote the start of The Next Doctor to have the TARDIS land in 1851 at random. It would now be implied that some time had elapsed between the events of the two episodes, which resolved the difficulty that, if the action was continuous, the Doctor would be rainsoaked at the beginning of the Christmas special.

The Next Doctor would be made on its own as the tenth and final production block of the Season Thirty recording schedule, which was dubbed the Christmas Block. Assigned to direct was Andy Goddard, who had previously handled six episodes of Torchwood across its first two seasons. With Collinson now having left Doctor Who, Susie Liggat would produce The Next Doctor; this was a job she had performed on several occasions when Collinson was unavailable, most recently on Block Seven, which had consisted of Turn Left. The pivotal role of the Other Doctor went to David Morrissey, a longtime friend of the Eighth Doctor, Paul McGann; he had previously co-starred with Tennant in the crime-drama-cum-musical Blackpool. Ironically, Morrissey's wife, Esther Freud, had battled the Cybermen herself, having played a Cryon named Threst in 1985's Attack Of The Cybermen.

Following a week off after the conclusion of work on The Stolen Earth / Journey's End, filming for The Next Doctor began on April 7th and 8th at Fonmon Castle. Reverend Fairchild's residence was represented by the fortification in the hamlet of Fonmon, parts of which dated to the twelfth century. The 9th and 10th were spent at St Woolos Cemetery in Newport, which was the site of the massacre at the Reverend's funeral. April 11th took cast and crew to Doctor Who's usual studio home in Upper Boat, for the scenes of the Doctor in his counterpart's “TARDIS”.

Meanwhile, Tennant had met with incoming showrunner Steven Moffat to discuss his plans for Doctor Who. It had been generally assumed by the production team that the last of the specials would also be Tennant's final adventure as the Doctor, and the actor had certainly been so inclined by the end of 2007. A devoted fan of the programme, Tennant was becoming concerned that he might be tempted to overstay his welcome as the Doctor, and he was keen neither to let the show atrophy nor his own career stagnate. Nonetheless, Tennant had been impressed with Moffat's scripts for Doctor Who to date, and he now found himself enthused by what was revealed to him about Season Thirty-One. Working under the assumption that Tennant would remain for at most one additional year, Moffat explained that the premiere's opening minutes would depict the Doctor on the verge of regenerating. The rest of the season would then follow a slightly younger Doctor, gradually chronicling the events which led up to his final moments. Although Tennant found himself seriously tempted to stay on, Moffat would need a decision quickly, since he had to begin finalising the season's structure.

Work on The Next Doctor resumed after a day off on Sunday the 12th. On April 13th and 14th, material in the courtyard where the two Doctors first met was recorded at The Maltings in Cardiff Bay. The building into which they were dragged by the Cybershade was actually MOD Caerwent, which was now principally used as a training area; filming there took place on the 15th. The next day, Tennant met with Moffat and Piers Wenger, who had been appointed Gardner's successor. Tennant informed them that he had reluctantly decided to keep to his original plan and leave Doctor Who after the specials. As such, Season Thirty-One would introduce a completely new team, both behind and in front of the cameras.

Julie Gardner lobbied for the montage of all ten Doctors as a Christmas gift for the programme's fans

April 16th and 17th saw Tredegar House in Newport serve as the Other Doctor's factory hideout. Material recorded there included the scene where the infostamp displayed a montage of all ten Doctors. Davies had originally written that only images of the Tenth Doctor would be projected, but Gardner lobbied for a more comprehensive overview of the Time Lord's past, which she thought would be a nice Christmas gift for the programme's fans. The clips shown included the First Doctor from The Time Meddler, the Second Doctor from The Ice Warriors, the Third Doctor from Terror Of The Autons, the Fourth Doctor from City Of Death, the Fifth Doctor from Arc Of Infinity, the Sixth Doctor from the first segment of The Trial Of A Time Lord, the Seventh Doctor from Time And The Rani, the Eighth Doctor from Doctor Who (1996), the Ninth Doctor from The Parting Of The Ways, and the Tenth Doctor from The Family Of Blood. On April 18th, the scenes in the cellar and tunnels were recorded at Hensol Castle in Hensol, before another pause on Saturday the 19th.

Goddard's team spent much of the subsequent week at Gloucester in Gloucestershire. The focus was on scenes in the London streets, which were chiefly recorded in the vicinity of Millers Green, College Green and Gloucester Cathedral from April 20th to 22nd, and then along nearby Berkeley Street on the 23rd. It was back to Wales on the 24th, when the docklands street outside the Cyberman base was actually located at Shire Hall in Monmouth. April 25th saw cast and crew return to Tredegar House for the scenes with the moored “TARDIS” and additional street footage.

Following the weekend, the remainder of principal photography was confined to Upper Boat. From April 28th to 30th, Goddard recorded the material in the Cybermen's headquarters. This was actually the standing set for the Hub from the spin-off series Torchwood, which Davies ensured was completely redressed to mask its identity. Green screen footage was also shot on the 30th, and this work carried over to May 1st, when scenes in the TARDIS console room and the tunnels were also recorded, alongside various inserts. More pick-up shots were taped on the 2nd, as were sequences in the CyberKing chamber. The original prop for Miss Hartigan's crown had been found to strongly resemble the headpiece worn by the ill-fated Lisa in the 2006 Torchwood episode Cyberwoman, and had now been altered. Finally, Goddard began recording scenes on the CyberKing throne; this work continued to May 3rd, which marked the end of the exhausting ten-month production calendar. It also saw Liggat's departure from Doctor Who, as she had now decided that she was not interested in occupying the producer's chair full-time. She moved onto a variety of other projects, including House Of Anubis, The Cafe and an episode of Moffat's Sherlock.

A notable edit saw the Doctor use a stethoscope to establish that the Other Doctor had just one heart

Recording for Doctor Who now stood down for its longest hiatus since the programme's revival. However, there was still post-production to be completed for The Next Doctor. A notable edit was the elimination of a sequence on the staircase at Reverend Fairchild's house, in which the Doctor used a stethoscope to establish that the Other Doctor had just one heart. It was now felt that too much suspense would be squandered if it was revealed so early that the Other Doctor was human. At one stage, it was thought that Murray Gold would provide an original Christmas hymn for The Next Doctor, to be heard during the early scenes in which the Doctor explored Victorian London. He had written songs for each of the first three Doctor Who Christmas specials, but ultimately would not do so for The Next Doctor.

Over the summer, there was considerable discussion amongst the BBC and both the outgoing and incoming production teams as to how and when Tennant's forthcoming departure should be announced. Moffat would soon need to begin auditions for the role of the Eleventh Doctor, and there was enormous concern that these interviews would be leaked to the press, effectively giving the game away. As it happened, Tennant was amongst the nominees for the National Television Awards, held at the end of October. The actor suggested an audacious plan: in the event that he won the trophy, he would unveil his decision to step down from Doctor Who as part of his acceptance speech. It was soon realised that Tennant would not be able to attend the NTA ceremony due to his commitments to Hamlet, but it was agreed that a live link to the theatre at Stratford could be arranged instead. With the cooperation of the NTA producers, the announcement of the winner would be timed to coincide with the interval of Hamlet, affording Tennant the opportunity to appear before the live television audience.

The plan was put into action, with the utmost secrecy maintained. It was even jokingly labelled “Operation COBRA”, after the government crisis response committee which took its name from Cabinet Office Briefing Room Alpha at Whitehall. During the NTA ceremony on October 29th, Tennant was indeed announced as the recipient of the Outstanding Drama Performance prize. Moments later, the nation watched as he graciously accepted the award... and then acknowledged that, when Doctor Who returned for its next full season in 2010, it would be with a new Doctor at the helm of the TARDIS.

By December, Steven Moffat and Piers Wenger had decided to offer Matt Smith the starring role in Doctor Who

Given the timing of Tennant's announcement and the near-contemporaneous revelation of the title of the Christmas special, press interest in The Next Doctor was fever-pitched. Indeed, there was considerable speculation that Morrissey had actually been cast as the Eleventh Doctor. Appetites were further whetted when the pre-credits sequence was broadcast on November 14th as part of the Children In Need charity appeal. In reality, the new Doctor had not yet been chosen; in fact, Moffat and Wenger would not start meeting with candidates until the following week. Moffat's impulse was to cast a more mature performer in the role, but he and Wenger were captivated by the audition of an actor even younger than Tennant: twenty-six-year-old Matt Smith. By December, Moffat and Wenger had decided to offer Smith the starring role in Doctor Who; on December 10th, the identity of the Eleventh Doctor was revealed to Davies.

Amidst all of the speculation about the future of Doctor Who, The Next Doctor aired on Christmas Day to an audience only slightly smaller than 2007's Voyage Of The Damned, which had been bolstered by Kylie Minogue's involvement as Astrid Peth. For the second year in a row, only one programme had more viewers than Doctor Who during the festive week; this time it was the premiere of the short film Wallace And Gromit in A Matter Of Loaf And Death.

But with the Other Doctor revealed not as the Time Lord's new regeneration but as an amnesiac Jackson Lake, curiosity about Doctor Who's next lead actor was still cresting. Finally, in an unprecedented move, a half-hour block of the BBC One schedule on January 3rd, 2009 was reserved for a special edition of the documentary programme Doctor Who Confidential. Originally billed as a retrospective of the first ten Doctors, it was announced on January 2nd that the broadcast would, in fact, see the revelation of the Eleventh Doctor's identity. Twenty-four hours later, with more than six million people watching, Matt Smith was unveiled to the world as Tennant's successor. The countdown was under way to a brand new era for Doctor Who...

• Doctor Who Magazine Special Edition #25, 8th July 2010, “The Next Doctor” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #60, 2018, “Story 199: The Next Doctor”, edited by Mark Wright, Hachette Partworks Ltd.
• Doctor Who: The Writer's Tale -- The Final Chapter by Russell T Davies and Benjamin Cook (2010), BBC Books.