Interesting comments. Thinking about it some more, saying that "the original melody ... gets completely lost" was wrong - the tune of Three Pretty Boys, or Bellamy's version of Lemady, is right there.

What gets lost is the beat. I imagine that PB would snort at the idea that a folk song has a beat in the first place, but I think if you listen to a lot of source singers you can hear how many beats there are in the bar and where the accent falls - even while that structure is being pulled out of shape where the words demand it (3 beats instead of 4 in this line, 5 instead of 4 in that one). To take another 'Revival' singer, Tony Capstick clearly had a metronome in his head - listening to his unaccompanied recordings (Van Diemen's Land, the Scarecrow, Old Molly Metcalf) you can hear where the accent falls at all times, even when he's singing against it.

Bellamy clearly could sing (and write!) a rhythmically regular tune when he wanted to - Down the Moor, Anchor Song. I suppose what intrigues me is that, quite a lot of the time, he didn't want to. And it does make him hard to follow. (I spent about twelve weeks with PB's Lemady: six weeks to learn how he did what he did, six weeks to learn how not to do it - or at least how to keep it in reserve.) But I guess that - as a couple of people have said - when we want guidance on how to sing these songs, it's not interpreters like PB who we should be looking to.