David TennantIt's no secret that The Doctor will be battling old enemies the Cybermen in ye-olde Victorian London this Christmas.

But it turns out that show producer Russell T Davies had another wizard idea that was vetoed by David Tennant.

In an extract from his forthcoming book, Doctor Who: The Writer's Tale, Russell reveals how he wanted to bring in Harry Potter author JK Rowling for a one off Crimbo spesh.

Russell explained his idea in an email to journalist and co-writer Benjamin Cook: "Zap. JK's imagination becomes real. The Doctor arrives and has to battle through a world of witches and wizards, with wands and spells, to reach JK Rowling at the heart of it all."

The writer goes on to reveal that his suggestion went down like a tonne of bricks with his leading actor:  "David doesn't like the JK idea. He thinks it sounds like a spoof so we've paused slightly, wondering whether to win him round or just abandon something 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."

Russell also reignited the debate over who will replace David Tennant when the Doctor next regenerates.

The show boss said that actor Russell Tovey, who appeared as a crew member on the spaceship Titanic in the 2007 Christmas special Voyage Of The Damned, would be his choice:

"He's going to be huge, that man. He's amazing. I think I'd make him the Eleventh Doctor."