“So I was in the office looking over a script Mark had sent me when I got this call from downstairs saying someone was here to see me. Naturally I told them to wait, but then into my office quite literally teleported Wendy Hawthorne and Derek Smythe. Now as you can imagine I was quite shocked by this, but when that wore off and we started talking we got into some really deep stuff.
Wendy, see, was a Wytch and knew about actual time travel - apparently she'd been off travelling the world in a camper van and when I looked it up I found that she'd been demolishing mercury mines and setting up proper refugee centres and training people to deal with AIDS epidemics. She was being the doctor that the Doctor always wanted to be, and it dawned on me that the show had really taken a different turn recently, and so I called up Mark, called up Peter and we had a long talk with Wendy, and eventually we decided to scrap the whole script for Series 9 and rewrite it.
Now that upset quite a lot of fans at first, but I think it's something we really had to do, and Peter was with me on it, and so we reshaped the show based on what Wendy had told us, and what she and Derek had been up to in her camper van, and shot the new format and it was a massive success! With a Chronomancer's advice we managed to finally do away with the 'timey wimey' explanation for everything and the show was better for being grounded in actual time travel, and the role model set by Twelve's new work saving lives as a proper purpose really made Series 9 to 12 unforgettable.
So thank you Wendy, and thank you Derek - Doctor Who would never have reached 75 without you.”
- Steven Moffat talking on UKBC Radio One as part of the Doctor Who 75th Anniversary Celebrations