Q. What was the genesis of this year’s Christmas special?

A. There had been a feeling that we needed a really, really Christmasy one, because the previous one had been David Tennant’s exit from the role. It had been quite dark and not as Christmasy as normal. We had wanted to reset it and make it a hugely jolly, merry one. Well, jolly, merry and a little bit sad.

Q. Is your story meant to be a loose nod to Dickens’s “Christmas Carol”?

A. Well, it’s called “A Christmas Carol.” It is “A Christmas Carol.”

Q. Why is that the story everyone turns to as source material at this time of the year?

A. I love “A Christmas Carol,” it’s a fantastic story. Even “It’s a Wonderful Life” is really sort of “A Christmas Carol.” Time travel at Christmas says “A Christmas Carol” and it says “Doctor Who.” The moment you think of it, if you have the Doctor as the Ghost of Christmas Past, it sort of makes sense.

Q. When did you film this episode?

A. When did we actually do it? Back in July. It was a long time ago.

Q. Was it strange trying to get into a holiday spirit in the middle of the summer?

A. Yeah, especially because I was writing it in April. I’d flown to Los Angeles while we were going on interviews [for the United States season premiere of “Doctor Who”] and got stuck there by the volcano. L.A. is just the least Christmasy place on earth. So I turned up the air-conditioning and played Christmas music to try to get in the frame of mind. But I’m used to thinking on different planets. Thinking about a different time of year wasn’t so bad. It was the smallest amount of time travel “Doctor Who” ever had to do.

Q. Your “Doctor Who” episodes often end with teases to the next story line, and this one ends in an especially tantalizing way  or is it meant to be a joke?