Purcell in Pride and Prejudice

I really should know this, but somebody help me out, sniggering deserved. In this lovely movie of last year, there is a variation on a really well known Purcell melody. It is rendered as violin solo. WHAT IS IT???

For any of you who do not know the answer AND have not seen the movie, please do. Great trees, good casting (Sutherland is actually not a jerk), camera work heavily influenced by "Russian Ark" in the ball sequence.
rent the movie and look up the credits at the end it usually gives all the music used, that will at least give you a start
Uru975, no help here, it is the guy who did the score in the credits. He did a variation on Purcell and therefore did not make a complete reference.