He spoke to RadioTimes.com about it:
“I think it’s nice to have someone who’s light-hearted and fun. And I think it’s good that the Doctor can be quite dark, sometimes, but you need someone to draw him out of that, and also to throw that into contrast. So someone who can run, scream and be quite glamorous — glamorous in any demanding situation.’
“I’ve always loved what [previous executive producer Russell T Davies] did with Billie Piper, because you hadn’t really had in DOCTOR WHO a very clear working-class voice. And I liked how Billie was very clearly someone who lived on an estate, and was a normal person. Which, in a way, the show hadn’t really done that before. It was of its time, in the sense that everyone spoke standard English, and it didn’t always reflect the real world. So I always like it when they have companions who reflect the real world – which Jenna does, because she’s from Blackpool. You can’t get more real-world than Blackpool!”
What does he think of the possibility — recently voiced by writer Mark Gatiss — that the next companion could be male?
“I quite like the idea of classic DOCTOR WHO, which I must probably identify as Jon Pertwee or Tom Baker. Which is Jon Pertwee with Katy Manning and Elisabeth Sladen; and Tom Baker with Elisabeth Sladen – I just think that combo of the slightly strange and alien Time Lord with the intelligent, enthusiastic and inquisitive girl is a good combo. I don’t know why – but it just seems to work. And also [the male-female partnership] has no romantic component, so I think it allows both characters to operate to their full extent. They’re never taken into a cul-de-sac of romance.”
Has Capaldi even been asked to give his opinion?
“Not so far. I will be [asked] at some point. I’m not quite sure where we are at the moment. But obviously at the end of the day it has to be somebody I’m happy with. Happy to work with. That will have to be looked to.”