Series 4 Cast Update

This news is taken from the Doctor Who Official Site
Monster role for Young Ones star (Series Four spoiler!)
Christopher Ryan, best known for playing super-cool Mike in the classic comedy series The Young Ones, is set for a guest-starring role in an upcoming Series Four adventure.
Ryan will play a Sontaran leader in the story, due to begin filming in the next few weeks.
"I'm absolutely delighted to be appearing in this new Doctor Who," Chris revealed. "The last time I appeared in Doctor Who was in 1986, Colin Baker was the Doctor and I was still a Young One."
The story in question was the Trial Of A Time Lord, where Chris starred as the slug-like Mentor Kiv alongside Trevor Laird, who played Martha's dad in 2007.
If you know your Who lore, the Sontarans will need no introduction. If you're a newer viewer, however, you may not know that the Sontarans are amongst the greatest villains from the classic series of Doctor Who.
A military, warlike species, able to clone vast armies of themselves, the Sontarans are locked into an eternal struggle with their enemies the Rutans.