He tells Cook: “I was in the shower on Saturday morning (you may avert your eyes), thinking about how much I'd enjoyed that last Harry Potter book, how I'd love to write something like that, remembering that, back in 2004, I asked J.K.Rowling to write an episode of Doctor Who, though she politely declined, and reflecting that we can't possibly get someone to star in next year's Christmas Special who's as famous as Kylie... when all those things coalesced.

“BAM! I thought, don't ask J.K. to write a Doctor Who, ask her to be in a Doctor Who! Imagine it. A cold Edinburgh Christmas Eve. J.K. Rowling walking through the snow, pursued by a journalist. ‘What are you going to write after Harry Potter?' Later, J.K. sits down to write. At the same time, a Space Bug, probably put there by the Rita Skeeter-type journalist [a character in Harry Potter], leaps on to her back. ZAP! J.K.'s imagination becomes real! A world of Victorian magic replaces the present-day world. The Doctor arrives and has to battle through a world of witches and wizards, with wands and spells and CGI wonders, to reach J.K. Rowling at the heart of it all.”

"That's either brilliant or more like a Blue Peter crossover. But worth trying. It's different, certainly. So, Julie [Gardener, executive producer] is trying to set up a meeting with J.K. ...Imagine those opening titles: DAVID TENNANT flying at you, then J.K.ROWLING!...Imagine the Doctor in a world of magic made real - that would be glorious. So, there we go. That's under way."

It was not to be, however. In an e-mail three weeks later, Davies says that [David] Tennant [the lead in the show] has other ideas. “David doesn't like the J.K. idea,” he writes. “He thinks it sounds like a spoof, so we've paused slightly, wondering whether to win him round or just abandon something that he's not going to be happy with. We've got to keep him happy. He keeps us happy. Plus, he might be right. So that idea has parked itself, while Julie tries to find ways to approach J.K. anyway. And I doubt we'd ever get J.K. - she doesn't need to do it - so Cybermen in the snow are hauling themselves back into my head."