It was recently revealed that Elisabeth Sladen, Thomas Knight, Anjli Mohindra and Daniel Anthony will all be going to film a special mini episode of The Sarah Jane Adventures on Thursday for Comic Relief which will broadcast on March 13th with David Tennant hosting the first hour with Davina McCall. Apparently the special mini episode will feature a well known comedian and an attack by Rednosicles!
Update (13th Feb): The famous comedian, Ronnie Corbett has been confirmed as a guest star, and executive producer Russell T Davies said, "It's an honour to get involved with Red Nose Day, and with Ronnie Corbett, K-9 and an old enemy's return, we can promise Sarah Jane Smith's most extraordinary adventure yet!"