I think what Vespaboy`s colleague was thinking of is that at the end credits they gave `information` as if it were a documentary - i.e. actual facts about the `cold war` ending mixed in with the fiction.
I believe it is a true story based on a book. David Jason was on Parkinson on Sat evening and he said that the original story involved an American Submarine and not a British one, he also said that he pinched the book from the props department and thought it looked good so read it and got it televised.