What can you tell us about the Doctor Who Christmas special this year?
Well the Christmas special is very Christmassy, which I’m sure everyone will be relieved to hear. It finds the Doctor in a Dickensian kind of world, in a Christmas card sort of world which he’s been brought to in order to do a favour for a king. So there’s quite a festive spirit to the episode. But the favour is more complex and isn’t exclusively for the benefit of the king, but more for the benefit of the king’s consort.

What is your favourite scene from this episode?
I have lots of favourite scenes from the Christmas episode, but I think being met by Matt Lucas on a wonderful wintery Dickensian street with the TARDIS covered in snow was delightful, because it was like a Doctor Who Christmas card. Matt is such a fabulously funny person to have around, so I loved that!

Do you like filming Christmas episodes?
Yes I do like them - last year’s was a bit scarier than this one, this is more openly festive. I like the idea of ghost stories at Christmas and frightening things seem to work rather well in the festive environment.

Would you like to see River Song return?
Yes of course, because Alex is fabulous and it’s always lovely to work with her.

Who is Nardole?
The character of Nardole is played by Matt Lucas so you can expect a lot of laughs and pathos. He is, as ever, a hugely loveable personality, a little naïve, a little out of his depth and quite cosmic.

What was it like to come back?
I was quite surprised when I was asked to come back, but I was happy to because I just thought it would be great fun. It’s such a great character, she’s become so beloved by lots of fans and I’ve had them saying it would be so great for her to come back and to see her interacting with Peter Capaldi’s Doctor. I was actually thrilled when Steven decided he wanted to explore that too.

What did you think of the script?
It’s a wonderful slapstick caper. There’s a lot of great laughs, there’s a lot of fabulous River one-liners. The fans are going to love the things she says and there’s a lot of play. They’re also fighting a very interesting alien played by Greg Davies. It’s a really great episode and Steven has done my character proud.

Has this episode been challenging?
I’ve been really lucky in this episode as River gets to do an awful lot. She gets to run around in snow, I’ve been flying and have done harness work against a green screen. She’s got quite a few husbands in this episode and there’s a lot of fabulous quick-fire dialogue between her and the Doctor. She gets to snog the most handsome man in the work, his character name is Ramone. It’s all going on!

What were your favourite moments during filming?
The favourite moment so far for me was stepping back on to the TARDIS, because the interior of it has changed yet again. I’ve been on two different TARDIS incarnations, and to walk into this one and know it’s a familiar space but at the same time it’s different, was great. I love this one - everything works which is really fun, I stand there pressing all the buttons, it’s great!

Can you give us an introduction to the episode you’ve written this year?
The Doctor is an all new man and has been for a while. It may have slipped his mind that out there, in a very tangled and complicated way, is his wife that has never seen this face before and doesn’t even know about this incarnation. We’re about to stand with the Doctor and see what River is like when she doesn’t know he’s looking. We’re about to see what River thinks of Matt Smith turning into Peter Capaldi.

What made you want to write this episode?
River Song meets the Capaldi Doctor, that’s got to be fun - I’d like to write that. That’s what made me want to write. I knew it had to be a big romp for Christmas day and there’s nothing like River Song to make that evident - River brings a whole storm of camp glamour to it.

Is it any different writing a Christmas episode of Doctor Who?
Yes, you need to have a bit of Christmas in it, but that’s never felt to me like a tremendous impediment, it’s a hook to hang it on. Sometimes we go very Christmassy - ‘A Christmas Carol’ was incredibly Christmassy, so was ‘The Doctor, the Widow and the Wardrobe’ and ‘The Snowmen’ had the appearance of Christmas without being very Christmassy. Last Christmas is actually the least Christmassy episode we’ve ever done, except for the fact it actually had Santa Claus in it - I rather loved last Christmas. This year’s episode starts Christmassy and has a comedy romp!

Do you enjoy writing a Christmas episode?
I like Christmas specials - I know some people don’t. Some friends of mine don’t like Christmas specials very much and they’re always complaining about all the tinsel, the goodwill and the twinkly stars, and the lovely snow on the rooftops. I love all that, I love Christmas as a day and as a festival. I love that it’s dark, twinkly and rich red, all those things I adore so it’s no hardship for me at all.

Who is King Hydroflax?
King Hydroflax is a very bad King, who as it turns out is mostly cyborg - in fact only his head has remained. He’s a vicious, terrible and deeply stupid man and a dreadful tyrant.