A science advisor is a member of the pre-production and production teams who advises the writers and actors on how best to realistically portray scientific concepts on screen. Within DWU productions, they've largely gone uncredited. However John Sotos broke this pattern, receiving clear screen credit for his work on Torchwood: Miracle Day. His help was invaluable to that series, since it is largely based on a medical "what if?" situation.
Kit Pedler was an unofficial scientific advisor on Doctor Who during the late William Hartnell and early Patrick Troughton eras. He is especially known for giving scientific credibility to the concept of the Cybermen, and for prognosticating about the Internet in The War Machines. Likewise, Pip Baker's brother, a national defence scientist, was known to have been enlisted to help solve certain scientific dilemmas in The Trial of a Time Lord. (DCOM: The Ultimate Foe)