] Some time ago on this board someone suggested that Darcy was a whig. I'm afraid I couldn't grasp the reasoning,

That's my theory, arising from his family name of Fitzwilliam. Earl Fitzwilliam was the leading Whig magnate in JA's time, so my contention is that her contemporary readers would think `Ah, this guy's a Whig'.

Some links to earlier discussions:

http://www.pemberley.com/bin/archives/regarc.pl?read=31092

http://www.pemberley.com/bin/archives/regarc.pl?read=16694

http://www.pemberley.com/bin/archives/regarc.pl?read=3888