Usenet - uk.music.folk
Anyone who has an interest in the kind of music likely to be heard at a UK "Folk" event should read uk.music.folk.
Like most newsgroups these days, it gets its share of trolls, mischief-makers and flamewars but it has a solid core of regular posters who are very knowledgable and are willing to share their knowledge.
Just don't ask "What is Folk?" or you'll trigger multiple cries of "Horse!" (see the u.m.f. FAQ)