Not sure about drawing that firm a line around 'English', Tunesmith - particularly since it would demote some works collected by F. J. Child to second place! Me, I'd go for...

1. Trad. English or Scottish
2. Trad. Irish
3. Trad. American
4. "Contemporary folk" that sounds like it's at least on nodding terms with traditional forms
5. Music hall songs, parlour ballads, general daft stuff

In terms of proportions, 60% of the first and 10% each of the rest would do me fine. Well, I can dream.