During a Radio Times interview covering his final episode (contains light spoilers for the episode itself), Steven Moffat reveals that "they" (presumably the BBC) wanted Carey Mulligan to become a full-time companion as Sally Sparrow but she turned it down. It was the same with Carey Mulligan as Sally Sparrow in Blink (the Weeping Angels’ debut and Radio Times readers’ favourite episode). Oh my God, Carey Mulligan! It’s funny but Blink, I say immodestly, is a very famous episode of television and yet Carey Mulligan, who was the star of it, I’m almost certain wouldn’t even remember being in Doctor Who. I don’t think she was much of a fan, or anything. They liked her so much, they said, “Do you want to be the next companion?” but she said no. God, she was amazing. So you’ve never tried to get her back in any capacity? No. I know it’s a no. What a shame! I agree. But then does that character become more special because you never see her again? She just passes through the Doctor’s life. It’s surprising the people who do love being part of it. John Hurt loved being the Doctor and was quite insistent, asking, “Am I a real Doctor? Do I really count?” And we said, “Yes, you count. You’re on the poster. It is definitely you.” David Bradley is so thrilled that he is really the Doctor now. Because obviously he was sort of the Doctor in An Adventure in Space and Time . He’s been a star for ever, but being the Doctor is special, somehow. He’s a bit like Hartnell in a way. He’s got a mean face but he’s the nicest man alive, so sweet and generous. Honestly, as much as I love "Blink" and Carey Mulligan as Sally Sparrow, I never liked the idea of her as a full-time companion, so I'm glad she turned it down.