It is based somewhat on Adams's own college, St John's. For Shada, scenes at St. Cedd's were filmed on location at Emmanuel College.
St Cedd’s College ... owes a little to my memories of St John’s College, Cambridge, although I’ve also borrowed indiscriminately from other colleges as well. The point is that St Cedd’s College is a completely fictitious assemblage, and no correspondence is intended between any institutions or characters in this book and any real institutions or people, living, dead, or wandering the night in ghostly torment.
St Cedd's College is also mentioned in the Torchwood online game, made during the show's second series. It is said to be the college attended by Dr. John Winters, a fictional character within the game.