When did Peter Capaldi come on the radar for you?
"Quite a while back actually. I happened to know he's a very big fan of the show and there's something rather seductive about knowing that an utterly arresting-looking leading man actor is such a fan, so I'd started to think maybe we should do something about that. My shortlist consisted of Peter Capaldi and that's it! It was a very short shortlist. There was only one audition this time, and it wasn't an audition really. He just came around to my house and we put him on video to see what he'd look like as the Doctor and gosh, he was terribly good."

Are you disappointed the choice of Peter Capaldi sort of leaked online? And were you surprised how many people placed bets on it?
"Well I've made a tidy profit I can tell you! Look, compared to some of our recent leaks this has been comparatively minor! There are bigger scandals in the world to worry about than this."

Most fans have been positive and really seem to think Peter fits the bill as the Doctor...
"He had flicked through my mind when we were replacing David Tennant and he hadn't felt right then. But there's something that's right about the way Matt's Doctor paves the way for Peter's Doctor. It's one character going through his life played by a succession of different actors - so you can believe the strange 'Old/Young' Matt Smith will turn into the strange 'Young/Old' Peter Capaldi.

"Peter will bring the same brilliance as Matt I believe, but let's let Peter do that job. I'm going to write The Doctor, but I'm not going to tell him how to play The Doctor, and you'd be surprised how similar the Doctors are on paper when written. He's just going to have a new face and a new voice."

What in Peter's audition made you think he was The Doctor?
"I don't think it was anything in particular, I just think you know instantly when the Doctor is 'in the room', and those who I showed it to agreed that The Doctor was 'in the room'. And it was the same when Peter walked out on the live BBC1 Show, you could see that suddenly there was Peter as The Doctor. Malcolm Tucker (from The Thick Of It) was knocked out of the way, and here was this magnificent leading man."

Was there a conscious decision to go older with Peter's Doctor?
"Not particularly. The apparent age of the Doctor makes no narrative sense at all as he's been anything from his 20s to his 70s. Obviously he doesn't care, he just sort of gets a face off the rack and goes with it. I think it's good we've got a different age Doctor just because I cannot imagine what someone in their 20s could do with the Doctor after Matt Smith showed us how to be a 20s Doctor. I don't know what you'd do after that because he was so perfect. He'd have to be a total contradiction and it wouldn't work I don't think. So it makes life easier I suppose that Peter is different, but that wasn't the reason. The reason simply was when Peter turned up 'The Doctor was in the room'.

Peter Capaldi is such a big star, do you think you'll be able to keep him as The Doctor for a while?
"Yes I'd love to keep him! I'm thrilled to have him. Even with the minor hints out there on the internet beforehand, everyone seemed to be rapturous about the choice."

What's he been like playing The Doctor so far in the pieces you've given him?
"So far I've seen him do Doctor-ish stuff and he's magnificent. I've seen him deal with techno-babble and given him scenes that were deliberately impossible, with impossible dialogue and so on, just to see if he could do it, even without gunk and such-like being poured on him. We're working on it all."

Did you ever seriously consider a woman as the Doctor?
"It's absolutely narratively possible and when it's the right decision maybe we'll go with it. But to me, right now, I didn't feel it was right. In fact, not enough people wanted it, and most people who said they were dead against it were women! Not that I was influenced by that."