Key Points:

British actor David Tennant has announced he will quit science fiction show Doctor Who at the end of 2009.

The BBC confirmed Tennant, who has played the Time Lord since 2005, will film four special episodes before bowing out next year.

"I've had the most brilliant, bewildering and life-changing time working on Doctor Who," Tennant said.

"I have loved every day of it. It would be very easy to cling on to the Tardis console forever and I fear that if I don't take a deep breath and make the decision to move on now, then I simply never will."

"I don't want to outstay my welcome," he added.

Tennant's replacement has yet to be announced, but a fifth series of the hit show has been confirmed and scheduled for 2010.

The show's outgoing writer, Russell T Davies, said: "I've been lucky and honoured to work with David over the past few years - and it's not over yet, the Tenth Doctor still has five spectacular hours left!

"After which, I might drop an anvil on his head. Or maybe a piano. A radioactive piano.

"But we're planning the most enormous and spectacular ending, so keep watching," he added.