Just found out about the various extensions to RSS 2 that allow information about comments to be included in the RSS feeds.
I have revised my feed to include the full article along with links to the comments in it, numbers of comments etc. For more information on supporting comments in Moveable Type see this excellent HOWTO by Oleg Tkachenko.
The only caveat I would add is that you must remember to add the following namespace declarations to your RSS feed file (index.xml):-
xmlns:wfw="http://wellformedweb.org/CommentAPI/"
xmlns:slash="http://purl.org/rss/1.0/modules/slash/"
