Mark Gatiss has written for Doctor Who ever since the show returned to our screens in 2005 – that's nine adventures in 12 years. And now, sadly, it might all be over.

Having worked alongside both Russell T Davies and Steven Moffat, the League of Gentlemen star and Sherlock writer has suggested that his time working on the good Doctor might have come to an end, with Torchwood and Broadchurch chief Chris Chibnall ushering in a whole new era as showrunner from 2018.

With what might be his final contribution – an Ice Warriors vs. Victorian-era soldiers romp called 'The Empress of Mars' – airing this Saturday night, Digital Spy grilled Gatiss on reinventing classic monsters, Peter Capaldi's impending exit and what the future holds.

You've already had one crack at the Ice Warriors in 2013 episode 'Cold War'. What did you want to do with them this time?

"Well, I just said to Steven, everything's coming to an end, can I do the story I've always wanted to do, which is the Ice Warriors on Mars? I didn't actually have a story at that point [laughs]. I just always wanted to explore more of their backstory.

"Considering they were always such a big presence in Doctor Who, we know an extraordinarily small amount about them. And I found that doing 'Cold War', that it was rather thrilling to be able to create new things, to give them some backstory and history, just with occasional little windows onto things.

"And I thought, 'Well, we can do Mars, it's practicable.' They're a very cool monster – or a very cold monster – and I just wanted to do something new with them, which was to introduce the Ice Queen into the mythology."

BBC

Yes, this is the episode's big twist – how much can you say about this new type of Ice Warrior?

"It's not a twist, really, there's just a female one – and about bloody time, I would say! I thought that it would be an interesting thing to do – rather than just some frozen Ice Warriors, the usual thing, that there was a queen involved, and just give it a different slant, really.

"I have to say, it suddenly occurred me to that the Ice Warriors have such a history of being frozen and woken up after their time, I think they must've got their hibernation equipment from the same people who sold them to the Silurians!

"It's always the same: 'How long have I been asleep?' 'A lot longer than you think!' 'Oh shit, again?' It happens all the time!"

RELATED: Pearl Mackie "loved" Doctor Who series 10's "complex" Ice Warrior

It does seem like such a natural thing to do. Why do you think it has taken so long to set an Ice Warrior story on their home planet of Mars?

"It's taken more than 50 years, because [Ice Warriors creator] Brian Hayles's original second story, what became 'The Seeds of Death', was called 'Lords of the Red Planet' and it was precisely that.

"I'm sure it was to do with budget and scale. I mean, it took till [2009 episode] 'The Waters of Mars' to do an actual Doctor Who story on Mars, which is remarkable really when you think it's essentially a red desert, something that feels very achievable. Except my whole story's set underground, so we didn't even have to go up top.

"It's to do with scale – if you want to do Ice Warrior society, you have to do a fragment of it. We just don't have the budget to do a whole city on the surface, with thousands of Ice Warriors and different levels of society.

"So as is always the way with Doctor Who, and as it should be, it becomes a sort of 'bottle story' of what's happened to this particular group, in this particular part of Mars, without having to do the whole of Mars. Though that would be lovely, wouldn't it?"

This content is imported from YouTube. You may be able to find the same content in another format, or you may be able to find more information, at their web site.

With the human race as the invaders of Mars, is this veering more on the 'Curse of Peladon' side of things? Are the Ice Warriors perhaps not the villains of this episode?

"Wait and see… But the thing I was very keen to explore – some of the lines have been cut, actually, but it's sort of there in the DNA of it, especially with Bill being a new companion – is not to make assumptions about which side the Doctor will take.

"The Ice Warriors were really the first Doctor Who monster where the plot twist was that they turned out to be the good guy, and [1972 Jon Pertwee serial] 'Curse of Peladon' [below] is one of my formative influences. It casts a very long shadow in that sense.

BBC

"You might just assume that the hissing green monsters are going to turn out to be the baddies, and they're not. So I really think that's an interesting thing to explore – that there might be different factions and different politics, depending on where they are in their history, just like us.

"I mean, who'd have thought in the last 20 years we'd have turned into this shit-show that we are now? Who would've predicted any of this? Nothing surprises me anymore. I wouldn't be surprised if we actually found an Ice Warrior!"

Speaking about Bill in this episode, how did you find writing for the character – and how much did you have to go on when starting 'The Empress of Mars'?

"I'd read 'The Pilot' and 'Smile', I think, and I'd seen a bit of footage – and obviously that little clip they shot to introduce her.

"But also, Steven and I were in Morocco last year writing Sherlock, as he was writing the audition stuff for it, so we talked a lot about what he wanted to do with the character and where she was gonna come from, and just the whole idea of the sort of 'soft reboot', so that was very much in my mind."

This series feels as though it really has gone back to basics and stripped Doctor Who down to its essentials. Was that something that was discussed a lot in the planning? Or was it just the consequence of having a new companion?

"No, it was a definite decision. Obviously, with a new companion, you always slightly see the show through different eyes, but I think there was a conscious effort with Bill to make her... it is like coming into the junkyard right at the beginning and seeing it all again.

"Partly, there's the fun of just asking the most basic questions. I'm afraid it was my idea to have her ask where the loos are [in the TARDIS], because it's always bothered me that nobody's ever asked that! And actually, it's part of the thing that grounds it – if it happened to you, what would you think?

BBC

"So there's that, but equally, Clara (Jenna Coleman) was a much more complex character who turned out to be full of secrets, whereas Bill is a lot more straightforward and I think that's crucial to the notion of a reboot, a soft reboot, that you don't overcomplicate the companion with lots of extra baggage, just in order to say, 'Oh, this companion is different to all the others.'

"It's exactly like with Billie [Piper] right at the beginning of Russell's time – you want to see Doctor Who through the eyes of an ordinary person, because then you see how exotic and strange it is. If you try and make the companion exotic and strange, then there's too much going on."

No matter what happens in the future, we know this is definitely your last episode for Peter Capaldi's Doctor. Was that something you knew when you were writing it?

"Not definitely, no. Not definitely. I suspected it would be. It does feel a bit like living in the pages of The Making of Doctor Who, it really does, and all those things that we all grew up with as sort of holy writ are actually happening to us as real people.

"So I suspected that Peter would want to go with Steven because it just felt like time, and I think that does happen. Something that Doctor Who fans, I think, rarely take in as part of the equation is the human element – as the Daleks might say. The fact that there are lots of human emotions in the mix here.

"Part of you, of course, would love to see Peter under Chris Chibnall. David [Tennant] nearly stayed, and David under Steven for a year would've been such a different beast, it's fascinating to think. But, those are the arguments that Doctor Who fans have in the pub, not the ones that actors have when they feel like it's time to go."

How are you feeling about Peter leaving?

"It's a mixture. I think Peter's been magnificent. I love him this year – I think he's just completely in his groove. He looks brilliant, I think the season is excellent – really refreshing and fun – and I think he's just on fire, really. So it's a great way to go.

"But obviously I'll be very sad to see him go. I think he's been amazing... and I can't believe how quickly it's gone. It's been him as long as Hartnell and Troughton were the Doctor, it just seems like the blink of an eye since the last time.

BBC

"But the show depends on change – not just the new Doctor but a whole new approach and a new team. It's always exciting and a little frightening, but also thrilling because there's all that to look forward to. So I can't wait to see who [the new Doctor] is – but I have no idea who it is."

And if this is the end of your own involvement with the series, do you have one episode that you've written that you're particularly proud of?

"Oh Lord! I think my favourite is probably 'The Crimson Horror' – I think it's the most me. I loved doing everything about it, from asking Diana Rigg and Rachael Stirling to do it, and writing it for them... it was so much fun.

"And I was genuinely proud of doing a Northern Doctor Who. It's occurred to me many times that actual local geography has not been explored enough in the show, never mind extra-terrestrially. It's amazing what a difference it makes to the tone of a programme if it's set somewhere other than South East England... or Cardiff. So I loved doing that one.

"But I would say my proudest achievement is [2013's William Hartnell biopic] An Adventure in Space and Time. Definitely. It's my love letter to the whole show in every aspect of its life. So if this is the end, then the moment has been prepared for."

Doctor Who, 'The Empress of Mars', airs this Saturday (June 10) at 7.15pm on BBC One.

Want up-to-the-minute entertainment and tech news? Just hit 'Like' on our Digital Spy Facebook page and 'Follow' on our @digitalspy Twitter account and you're all set.

This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io