"Peter Bellamy used the term 'Tradition Idiom'"
That's not a bad term to use to discriminate between the imitations and the real thing - I agree entirely that Peter was one singer who was well aware of the difference.
"maintaining a tradition"
Maintaining a tradition is fine, using traditional forms to create new songs is a wonderful way of doing that

Hi Jim, me again ;) Can I just say I'm enjoying this debate and thank you for indulging me!

So we seem to be in agreement that new songs that are influenced by, or show respect to the tradition is fine, but I still want to know what we call them?

These new songs (and/or tunes) written using traditional forms are certainly not pop, rock, rap, jazz etc etc if we can't call them 'folk' then what do we call them?

John