Clara discovers a man who claims to be Santa Claus on her rooftop, leading to a reunion with the Doctor. Before long, they find themselves at the North Pole, where a scientific research base has become infested with Kantrofarri. Also known as Dream Crabs, the creatures attach themselves to a victim and induce a state of euphoric reverie, all while slowly devouring their host. When Clara is attacked by a Dream Crab and believes herself to be celebrating Christmas Day with Danny Pink, the Doctor turns to Santa for help. But how can dreamers ever recognise that they are dreaming?

The 2014 Doctor Who Christmas special would mark the tenth edition of what had now become an annual BBC event. Over the course of the preceding decade, many traditions associated with the holiday had been given a Doctor Who twist. An exception, however, was Santa Claus: his appearance had been adopted by evil robots in 2005's The Christmas Invasion and 2006's The Runaway Bride, and the Eleventh Doctor had made an offhand reference to him during 2010's A Christmas Carol, but the jolly old elf also known as Kris Kringle had otherwise been absent from Doctor Who's yuletide adventures.

Although Santa had his roots in more ancient folklore, it was the nineteenth and twentieth centuries which saw the legend emerge of a bearded man in red and white, who visited on Christmas Eve to deliver presents to good children. Santa was effectively a combination of two existing figures. One was Father Christmas, who had his origins in seventeenth-century England, and was now perhaps best-known as the model for the Ghost of Christmas Present in Charles Dickens' 1843 novel A Christmas Carol. The other was the fourth-century Saint Nicholas of Myra who, amongst other associations, was the patron saint of children. Indeed, Saint Nicholas had already inspired the Dutch tradition of Sinterklaas, which also informed Santa Claus and was the source of his name.

The image of Santa Claus began to coalesce with the 1823 publication of A Visit From St Nicholas

The image of Santa Claus began to coalesce with the 1823 publication of the poem A Visit From St Nicholas, subsequently known as The Night Before Christmas. Also highly influential was the 1860s artwork of Thomas Nast; the placement of Santa's toy workshop at the North Pole may have been Nast's invention. The notion of the workshop being staffed by elves was popularised by an 1873 edition of the magazine Godey's Lady's Book. Santa's physical appearance became more consistent in the early part of the twentieth century, thanks in part to his inclusion in publicity campaigns by companies like Coca Cola. More additions to the mythology soon emerged; amongst them was Rudolph the Red-Nosed Reindeer, created for a 1939 poem by Robert L May.

Doctor Who executive producer Steven Moffat felt that an on-screen meeting between the Doctor and Santa Claus was long overdue. He thought that it would suit a new twist on a concept already employed by Simon Nye for 2010's Amy's Choice: the uncertainty which could sometimes be felt about whether a sleeper has awoken or is still dreaming. This notion had taken on a new relevance with the popularity of the 2010 blockbuster Inception, about a team of agents that could insert themselves into people's dreams. Several other movies also helped influence Moffat's narrative. The Kantrofarri were inspired by the face-hugging parasite in the 1979 science-fiction classic Alien. The scientific installation was drawn from the polar facilities of 1951's The Thing From Another World and its 1982 remake, The Thing; both were based on John W Campbell Jr's Antarctic-set novella Who Goes There? (1938). Moffat also looked to the 1947 Christmas film Miracle On 34th Street, which featured a man who claimed to be Santa and overcame his detractors to prove that he was the genuine article.

Moffat began writing the script for the Christmas special during July 2014. Originally, the Doctor saved Professor Albert from being killed by the Sleepers as they emerged through the monitor screens. When Albert then woke up in the real world, he was revealed to be a lavatory attendant. The Kantrofarri were envisaged as living outside the chronological progression of history, with Bellows actually hailing from 1890. All of the movies which had directly inspired Moffat appeared on Shona's itinerary of DVDs to watch; Moffat also considered having the list feature a cheeky reference to Blink, his popular 2007 Doctor Who story, but he quickly decided that it would be too self-congratulatory.

Jenna Coleman had intended to leave Doctor Who at the end of Season 34, but wanted to continue working with Peter Capaldi

A major element of the storyline was the departure of Clara Oswald. Actress Jenna Coleman had originally intended to leave Doctor Who at the end of Season Thirty-Four, but she had decided to stay for the Christmas special because she wanted to continue working with Peter Capaldi. As such, the first draft ended with the Doctor bidding farewell to the aged Clara. There was then a dream sequence in which Clara imagined herself ascending the spiral staircase which had led to the TARDIS in the 2012 Christmas special, The Snowmen. As she climbed the steps, her form shifted between the various echoes of Clara which had been seen during Season Thirty-Three. She finally became the younger Clara who had travelled with the Doctor, and smiled as the TARDIS flew past on its way to the stars. This coda adapted an idea which Moffat had originally conceived for the end of The Day Of The Doctor, the fiftieth-anniversary special broadcast in 2013.

Assigned to direct the Christmas special was Paul Wilmshurst, who had made Kill The Moon and Mummy On The Orient Express for Season Thirty-Four. So eager was Wilmshurst to return to Doctor Who that he cancelled a family vacation to ensure his availability. At an early stage, he hoped that the budget might permit location filming in Iceland for the North Pole exteriors, but this did not prove to be feasible. Amongst the cast was Dan Starkey; having previously appeared under prosthetics as various Sontarans, including the Doctor's occasional ally Commander Strax, he would finally perform with his face uncovered as Ian the elf. The role of Professor Albert went to Michael Troughton. He was the son of Patrick Troughton, who had starred as the Second Doctor, and the brother of David Troughton, who had been in four Doctor Who stories. The key role of Santa Claus would be played by Nick Frost, who was well known for movies like Shaun Of The Dead and television programmes such as Spaced.

Production on Doctor Who had stood down after the completion of Season Thirty-Four in early August, allowing Capaldi and Coleman to participate in various publicity exercises to promote its forthcoming broadcast. A highlight was an international tour, spanning August 7th to 18th, during which Capaldi encouraged Coleman to stay on Doctor Who for another year. After participating in the readthrough of the Christmas special on September 3rd, Coleman informed Moffat that she had changed her mind, and wanted to remain for Season Thirty-Five. Moffat was delighted and, in fact, he had already prepared an alternative draft in which the meeting with the aged Clara was revealed to be another dream. Work on a possible replacement companion -- who had already been incorporated into some scripts for Season Thirty-Five -- was abandoned. Also changed at a late stage was the earworm which Shona sang as she tried to navigate between the Sleepers. It was originally scripted to be the 1934 standard Santa Claus Is Comin' To Town but, when rights to the lyrics proved to be more expensive to obtain than anticipated, Moffat substituted Slade's 1973 hit Merry Xmas Everybody, which had already been heard in several previous Doctor Who stories.

As Santa Claus, Nick Frost's own beard was coloured white with make-up

Recording on the Christmas special began on September 8th at Roath Lock Studios in Cardiff, with Wilmshurst concentrating on early material in the polar base's control room. Vaendre Hall, a private residence in Cardiff, posed as Clara's house on the 9th and 10th, with Frost making his debut as Santa Claus on the latter day. Because he was recording scenes for the movie Unfinished Business during his work on Doctor Who, it was agreed that Frost's own beard would be coloured white with make-up, as opposed to the normal approach of applying a fake beard to his clean-shaven face. More control room sequences were then taped at Roath Lock on September 11th and 12th, prior to a day off on Saturday the 13th.

The same set featured during the early part of September 14th, before Wilmshurst turned his attention to action in the laboratory; this work continued on the 15th. It was back to Vaendre Hall on the 16th and 17th, which marked Samuel Anderson's final recording for Doctor Who as Danny Pink. The location again represented Clara's home, with Coleman in old age make-up on the first day, during which the sequence of Bellows waking up in her wheelchair was also filmed. Cast and crew returned to Roath Lock on September 18th. Shona walking along the corridor to the infirmary was taped first, after which she awoke in her apartment -- actually a standing set built for the Welsh-language soap opera Pobol y Cwm. The day concluded with Ashley waking up in her bedroom; some consideration had been given to shooting this scene on location.

The rest of the Christmas special was almost entirely made at Roath Lock, starting after a long weekend which spanned Friday to Sunday. September 22nd was chiefly devoted to sequences in the Arctic plains outside the polar base, although inserts were also shot on the infirmary set. The remaining material in the control room was completed on the 23rd, with Wilmshurst focussing on the infirmary on the 24th and 25th. The only excursion away from the studio during the latter part of the shoot took place on September 26th, when the cameras were rolling on a more extensive version of the snowscape in a hangar at MOD St Athan.

After the weekend, September 29th was spent back in the infirmary. The scenes aboard Santa's sleigh were taped on the 30th against a green screen. October 1st saw Wilmshurst capture more action in the laboratory, as well as various pick-up shots. The 2nd was dedicated to material on Clara's rooftop. Finally, the TARDIS sequence was recorded on October 3rd alongside the outstanding laboratory footage, the Doctor awakening on the alien world, and a number of inserts.

The special was ultimately given the title Last Christmas. It shared its name with the classic Wham! song, originally released in 1984. Over the years, the single had been covered by a variety of artists, amongst them former Doctor Who star Billie Piper, who had played companion Rose Tyler. Her version of Last Christmas was released as a B-side to her 1998 hit She Wants You. Meanwhile, at a Royal Television Society event on November 11th, Moffat and his fellow executive producer, Brian Minchin, confirmed that development was under way on Doctor Who's thirty-fifth season.

• The Doctor Who Companion -- The Twelfth Doctor: Volume Three, February 2020, “Last Christmas” by Andrew Pixley, Panini UK Ltd.
• Doctor Who: The Complete History #80, 2018, “Story 253: Last Christmas”, edited by Mark Wright, Hachette Partworks Ltd.