Nick is third in google for Blair/Brown slash, but Michael Kelly's Page of Misery: Slash Fiction Archive lists slash fiction about Newsnight, Trumpton, Historians, Philosophers Psycoanalysts and Zoologists.
My fantasies are so tame.
Update: Seeing as though I have another week off work, why don't you suggest some celebs - singly, or as a possibly unlikely couple - and some scenarios and let's see if we can't write some slash fiction...?