Russell T davies has given a few hints regarding the 2009 gap year specials:
What everyone's missing is that there will be a new companion," the executive producer told The Times. "We've got a young female companion at Easter, and then a much older woman next Christmas - someone in her fifties or sixties. I love that."
He added: "It's made casting next year's four specials difficult because we're going.
"We don’t want to ruin anyone's chances of being the new [Series 5] companion by casting her for a one-off."