Doctor Who star David Tennant will be making a cameo appearance in the final episode of Extras. However Ricky Gervais and Stephen Merchant are remaining tight lipped about what the Scottish actor's role will be in the 80-minute Christmas special.

A member of the production team told The Sun: "David's a huge fan of the show and extremely popular, so we've signed him up. He'll be in good company as we're lining up some other great names."

Tennant joins an ever growing list of confirmed cameos. John Travolta, George Michael, Dean Gaffney, Clive Owen, Gordon Ramsay, Jonathan Ross, Vernon Kay, Hale and Pace, Steps star Lisa Scott, Chico and Lionel Blair are other stars rumored to be in the episode.

Ricky Gervais has been recording the promotional material for the special episode. It includes a trailer in which he fails miserably to pitch the idea for Extras to the Dragons' Den millionaire investors. Meanwhile at last night's GQ Magazine Men Of The Year awards Stephen Merchant was named comedian of the year.

Here's a not-particularly-revealing set report from Gervais and Merchant at Pinewood Studios on the first day of filming...