Truly Madly Deeply (1990)
Shown in full as part of Screen Two
Nina and Jamie (and his ghost friends) watch this on tv in one scene.
Alan references the movie while talking to the judge.
Reference in an $800 clue in the category "Adverbs"
Seen on Alan Rickman's IMDb page, which is shown
One of Ian Hislop's choices to go into Room 101 - a clip is shown (date scene).