Good pickup by Andy Sernovitz on Jamie Oliver's quest to healthify the U.K. (they still fry chocolate bars there, don't they?).
As Andy mentions, some great word of mouth ingredients in a simple cause-related website:
A Noble Purpose - communciated via a manifesto
A Call to Action - get the chain going 2 plates at a tme
A Simple Tool - breaking the activity down in chunks, easy on the eyes website
Feedback - showing how many people have accepted your challenge to meet at your table
I would also mention that the site succeeds by providing well-laid out supoporting information in a blog-style format, use of documentary video in context and mastery of the repeatable idea "Ministry of Food", "Pass it On" and "Get the Country Cooking Again".
Jamie - well done chap, heaven knows this needs to be that good - with trans-fatty crisps, big brewed ales and steak & kdiney pie as staples, you have a big challenge ahead of you.