Doctor Who is dead – long live Doctor Who!

A moment later, the rehearsal over, he’s laughing with David Bradley about the heat – “I’m getting a bit hot. I think my hair is going to ignite!” he says – then retires to a hidden corner, where he spends a good 15 minutes matching his line delivery with the incoming explosions.

“It’s very exhausting! Very exhausting – like dancing,” he tells us afterwards, laughing through his tiredness.

But Capaldi’s upbeat attitude belies the momentous nature of what he’s actually shooting. As we speak, he’s on his final few days of filming for Doctor Who’s Christmas special, which marks the end of not only his own time in the series but also showrunner Steven Moffat, who has been in charge since 2010.

Suffice it to say, this is a Big Deal – which is probably why Capaldi was originally much more emotional about the whole thing.

“His eyes were just brimming with tears, and it was obviously a hugely big deal for him,” Jo Whiley, a friend of Capaldi’s, tells me of the day the actor unexpectedly appeared on her BBC Radio 2 show last January to announce his departure.

“It was a very emotional experience to tell everyone that this was it, that this was his time to move on.”

Capaldi, a fan of the show since his childhood, who famously wrote eager letters to Radio Times magazine about his love for the series, had been rumoured to be on the way out ever since Moffat had announced his own departure the year before, but now it was certain – and his announcement finally sealed the end of an intriguing, formative period in the show’s history since Moffat took it over in 2010 with Eleventh Doctor Matt Smith as the lead (Smith left in 2013).

As I write, Doctor Who is a world-beating, international hit watched by tens of millions of people in up to 90 countries around the world, but only a few short years ago it was still just a cancelled curio only kept alive through the efforts of dedicated fans.

When I speak to him on the set of the Christmas special, frequent series writer and actor Mark Gatiss recalls the day in 2003 when he stumbled upon an exhibition in North Wales full of Doctor Who memorabilia, a pitiful sight that more or less convinced him the series’ original run from 1963 to 1989 would soon be forgotten.

“It turned out to be the last day it was open,” he recalled. “And I traipsed round – it was a third full of baffled children. And their less baffled parents. And it was so sort of shabby and sad.

“And at the end I thought, that's it now. That must be it. And about two months later the show came back! And that was 12, however many years ago now. What an extraordinary thought.”

The credit for this new lease of life of course really lies with Russell T Davies, who revived the series to great success in 2005. But it’s only fair to credit Moffat for steering it through more testing times, characterised by the slow death of linear TV viewing, resulting in lower overnight ratings, and other new challenges of the ever-changing digital age.

Davies and his classic Who predecessors rarely had to deal with online writers relentlessly dissecting every trailer, picture and quote like Moffat has during his time on the series (and for which I should probably personally apologise).

Meanwhile, the sort of on-demand TV that’s pulling more and more viewers away from traditional schedules was only in its infancy when he took over. Incredibly, Netflix hadn’t even launched in the UK until two years after Moffat took the reins and BBC iPlayer was a sprightly three years old. More generally, too, the Scottish screenwriter leaves the show in a radically different TV landscape than the one he started with.

And during this period, the ratings fell. The Doctor Who production team and certain fans have been bullish about the fixation on the show’s viewing figures for years, citing the changing viewing habits of the British public (who may now watch the episode at a far later date) and the show’s increased popularity abroad as caveats for the raw numbers – but no matter which way you look at it, fewer people in the UK are watching Doctor Who every year.

Steven Moffat’s first episode in charge (2010’s The Eleventh Hour) had consolidated viewing figures of around 10 million – his most recent story, series 10 finale the Doctor Falls, had about half that. And it’s the Moffat/Capaldi era of the last three years that has seen the biggest drop, possibly due to Capaldi’s older, more irascible Doctor being less popular with an audience who’d grown accustomed to younger, more romantic Time Lords like David Tennant and Matt Smith, or just the fact that by this point the series is either 53 or 12 years old depending on how you look at it, and no series can keep up massive viewing figures for that long.

“I remember when Peter Davison was cast, and it was like 'What? The Doctor's 29?? That's insane.’” Gatiss laughs. “And obviously as the mean age of the Doctor has come down, the radical thing to do off the back of David and Matt was to make the Doctor in his 50s.”

And then there’s been the fan reaction, with Moffat’s style of storytelling frequently attacked by detractors who have occasionally even accused him of misogyny for his treatment of female characters. The personal vitriol aimed at him, almost unprecedented for the largely anonymous role of TV writer, has even inspired a popular hashtag, #MoffatMustGo, which presumably will be mothballed after Monday’s episode when new boss Chris Chibnall takes over.

“Being visible as a writer is not… we are not designed by nature to be seen by people, let’s be honest,” Moffat reflected on the set of the Christmas special. “We should be concealed as far as possible.

“Being visible… I haven't really enjoyed that very much.”

The irony of all this is, of course, that the Russell T Davies era that fans now look back on so fondly was also roundly criticised by some viewers in its final few series, with many believing it to be over-emotional and character-driven and Whovians longing for the new dawn of Moffat (who at the time was known for writing the very best guest-penned episodes in modern Who).

“I did say to him ‘don't worry, because soon you will enter sainthood, because you'll stop,'" Gatiss told me earlier this year.

"As soon as you stop, as soon as it's the past, you're fine. And then it'll be Bring Back Moffat. Of course it will. Death to Chibnall. That's how it goes, isn’t it?”

And others of Moffat's collaborators are even more effusive.

“Steven will be remembered as the greatest Doctor Who writer that ever existed,” says Karen Gillan, who was one of the first people Moffat cast alongside Matt Smith for his first Doctor Who series.

“100 per cent, he's the best.”

“Oh, good lord, there's no doubt about it – he’s been magnificent,” Moffat’s predecessor Davies agrees, along with Capaldi who calls him “probably one of Doctor Who’s greatest writers”.

"He's done six seasons of Doctor Who, and that's no mean feat,” adds current companion Pearl Mackie. “To keep it fresh and keep it interesting, to keep people involved and engaged – I think that's a fantastic talent, and I hope that's what people will remember at the end of his tenure.”

And when you look at the huge achievements for which Moffat has been responsible – a 50th anniversary special that took a low budget and an impossible brief to create something that brought in huge viewing figures and delighted fans, a successful drive to increase the visibility of Doctor Who around the world and the writing of some of the most beautiful, ingenious episodes and characters the series has ever seen – it’s hard not to think the great annals of Whodom will judge him a little more kindly than many do now.

“I wondered what I'd be like in the final days as I fell from grace into the archives. I'm just really quite enjoying it,” Moffat says now of his final days on the series.

“I am enjoying talking to the new lot. I was here talking to them yesterday and they are all so excited and kind of nervous and that's lovely.

“For the first time, I think probably in about ten years, I don't have a deadline.”

Widespread appreciation for the Capaldi chapters of Moffat’s time in charge may be a little longer coming. While popular with some fans of both classic and modern Who, it’s fair to say that Capaldi’s time in the Tardis has been divisive, with the series’ attempt at a darker, more mature Time Lord (in contrast with Matt Smith’s younger, more upbeat Doctor) backfiring as viewers turned off in their droves (Capaldi's first episode in 2014 had 9.17 million consolidated viewers – his most recent in 2017, 5.3).

On the other hand, from a critical point of view it’s hard to say that Capaldi himself has been anything other than magnificent in the role, from his glorious one-hander episode Heaven Sent and beautifully-delivered speeches to his acceptance of the ambassadorial nature of playing the Doctor.

“It's a massive responsibility, you know – he signs all autographs, it's amazing,” Gatiss says. “We’re routinely 45 minutes late because Peter's signing everything.

“He was saying to me in the Tardis the other day, the most wonderful thing has been seeing kids' faces. He's exactly what the Doctor should be in real life and onscreen.”

“For us fans, he's the fan-made-good,” Davies adds. “A bit like David Tennant was as well. Imagine being that fan, running that fan club, writing those letters saying how much you loved it, drawing Daleks all your life, and then getting to play the Doctor!

“I mean I feel some of that because I was that fan and I got to write it, but to BE the Doctor, it's something actually quite extraordinary. It's brilliant. I mean, I'm sure he wouldn't mind my saying that he's already automatically the elder statesman of Doctor Who, simply by an accident of birth. And what a great title that is to have! Wonderful. Absolutely brilliant.”

By the most recent series it felt like Capaldi was finally in his groove, as reflected by positive reviews more or less across the board – but while the actor considered staying on with new boss Chibnall (“I’ll have to make up my mind, and I haven’t yet” he told me in 2016), he says he soon came to the realisation that it was the time for him to move along as well.

“I love this show, but I’ve never done anything where you turn up every day for ten months,” Capaldi told Radio Times earlier this year.

“I want to always be giving it my best and I don’t think if I stayed on I’d be able to do that. I can’t think of another way to say, ‘This could be the end of civilisation as we know it.'

“With episodic television of any genre, the audience wants the same thing all the time. But the instinct that leads the actor is not about being in a groove.”

And of course, ever since its first regeneration story in 1966’s The Tenth Planet (a serial being revisited in this week’s Christmas special, funnily enough) Doctor Who has been a series that thrived on change more than any other, and the next big step for the series – casting Broadchurch’s Jodie Whittaker as the first female incarnation of the Doctor – is already being touted as the shake-up the series needs to stay relevant in the modern age.

“To be asked to play the ultimate character, to get to play pretend in the truest form: this is why I wanted to be an actor in the first place,” Whittaker said in an early interview about her casting.

“To be able to play someone who is literally reinvented on screen, with all the freedoms that brings: what an unbelievable opportunity. And added to that, to be the first woman in that role.

“I’m beyond excited to begin this epic journey – with Chris and with every Whovian on this planet. It’s more than an honour to play the Doctor. It means remembering everyone I used to be, while stepping forward to embrace everything the Doctor stands for: hope. I can’t wait.”

“It just really keeps on going. It's like a show that has the perfect formula to never end, because you can change the characters and everybody's OK with it,” ex-companion Gillan adds.

“I think [Jodie] was the best, most perfect choice. She's an amazing actress. I can't wait to see what she does with the role.”

For the moment, though, fans are being left in a kind of limbo between two Doctor Who eras, being drip-fed costume and story details about Whittaker’s new Doctor while still preparing for Capaldi’s last stand. Still, it’s an inbetween state that will be over soon when Capaldi’s features blaze, glow and morph into Whittaker’s at the end of the Christmas special – and then the age of Jodie will truly begin.

“It's very odd – I was in the [BBC's] Roath Lock studios [in Cardiff] the other day, not for Doctor Who, for something else, and this interregnum is genuinely strange, because all the desks are deserted,” former showrunner Russell T Davies tells me.

“There were two lonely script editors sitting there. And all the design desks, all the production desks empty. It was proper leaving people notes on their desks to say hello, and it was a ghost ship.

“But you just know that, as of this week or very soon, all those desks will be filling up with workers.”

And when they do, they’ll be ushering in a whole new era of Doctor Who, which Moffat believes may be even more momentous than the one we’re leaving behind.

“There’s a huge amount of excitement in Jodie as the new Doctor,” he told Radio Times earlier this year. “It’s going to pep things up. [Doctor Who]’s going to be around for ever.

“There may be times – and these will not be bad times – when it goes off the air for a bit, but I’d almost be in favour of that now and then. To remind people that they miss it. I think it’s here for good. And it’s about to enter into a golden period.”

So perhaps, as we say goodbye to Peter Capaldi, Steven Moffat and their tumultuous, brilliant and flawed Doctor Who era once and for all, we should think back to some words – written by Moffat, and performed by Capaldi – from 2016 Christmas special The Return of Doctor Mysterio, when the Twelfth Doctor lays out a personal philosophy.

Things end. That's all. Everything ends, and it's always sad. But everything begins again too, and that's always happy.

Be happy. I'll look after everything else.

Doctor Who is dead. Long live Doctor Who!

Doctor Who: Twice Upon a Time airs on BBC1 on Christmas Day (Monday 25th December) at 5:30pm