By Tim Masters
Entertainment reporter, BBC News
Staying in the Tardis: David Tennant plays the 10th Doctor
Doctor Who star David Tennant has laughed off speculation that he is planning to quit the show at the end of the next series in 2008.
Comic actress Catherine Tate sparked rumours at the weekend when she said in a radio interview that she thought the next series would be Tennant's last.
Tate is due to join the Doctor in the Tardis as his new companion in 2008.
Tennant, speaking at the launch of the Christmas episode, said: "Catherine Tate stitched me up good and proper."
"I started getting all these phone calls on Saturday lunchtime saying apparently you're leaving Doctor Who," Tennant told the BBC. "Catherine Tate's just announced it on Radio 2 - thanks Catherine!"
He added: "I said to her on Monday morning did you know you've caused a minor diplomatic incident? She was completely oblivious that the phone had been ringing off the hook."
Tennant confirmed he was doing four Doctor Who specials in 2009, but there was no decision about the next series in 2010.
"I'm doing four more specials and beyond that no one's asked me to make any decisions and I'm quite happy to be enigmatic for as long as possible," he said.
The Christmas Day episode, Voyage Of The Damned, features Kylie Minogue as Astrid Peth, a waitress on board the Titanic.
Given the Doctor's form with his other companions it is no surprise that the two get to kiss during the adventure.
The special, which was screened before a celebrity audience at London's Science Museum, also features a new version of the theme tune.
The cast includes Geoffrey Palmer as the captain of the Titanic, and Bernard Cribbins - who featured in a big-screen Doctor Who adventure with Peter Cushing in 1966.
The audience included Work and Pensions Secretary Peter Hain who told the BBC afterwards: "It was absolutely awesome. Millions are going to be glued to their TV sets."
Doctor Who writer and executive producer Russell T Davies said: "I'm delighted with the next series, we're doing stuff we've never done before and it's bigger and better than before."
He said Kylie Minogue was keen to do more acting again.
"She did this because I think that's the way her thoughts are heading. She's missed it and fancied that discipline. I'd cast her again like that," he said.
Asked by a child in the audience whether evil Dalek creator Davros would be resurrected for the new series, Davies said: "I don't know. I'm as in the dark as you are. Would you like us to?"
Amid much laughter, he stroked his chin and added: "I'll see what I can do."