The official site has been updated with a video, narrated by Captain Jack Harkness, looking at the Weeping Angels - see it in the player above. Here's what the BBC say:
Christmas is a perfect time for scary stories that send a shiver down your spine and put a smile on your face! It's good to have a touch of terror in the tinsel and we've got a tale for you now that'll make you go brrrrrr!
But a warning to the curious... it's about a strange and terrifying race known as the Weeping Angels. Enjoy their story but whatever you do, don't blink!