"Sorry Richard, but he specifies that he regards folk sons as anything folk singers sing, so presumably if one o the singers happened to be a member of the local light opera society the Roud index would include selections from 'The Student Prince'"

That's not quite what Roud is saying. His message is that it is not a song's origins which make it 'folk', but what the folk have done with it. That is not the same as saying that anything sung by a 'folk singer' is therefore folk.

For Jim, it appears that an important aspect of folk song is that it shows that working- class culture is to be valued, and he is understandably sensitive to anything which seems to undermine this. Roud's interest is in how these songs evolved and how they were used. He doesn't appear to be particularly interested in making any claims either for or against working-class creativity. As I read it, he is not intending an attack on the working class, he is simply not taking a 'class-conscious' approach, perhaps in contrast to Harker and others, whose Marxist analysis he criticises strongly.