@ Jim Carroll, partly:

Given that these days the singing of traditional songs is largely the preserve of people involved in the folk scene than the public at large or regional or workplace communities and so on, there's a sound argument that any song taken up by and mutated within the folk scene is 'traditional' - because it has entered the folk community's own tradition and, in some cases, been sung by people who don't even know that it has a (relatively) recent origin. This could include those Cyril Tawney songs, Keith Marsden songs and Eric Bogle songs mentioned above as well as stuff like "the Testimony of Patience Kershaw", "The Dalesman's Litany" and "Farewell to the Gold". It could also include A.L. Lloyd's often excellent reimaginings of traditional songs. Of course, I know that none of these are traditional in the academic sense (with the exception of Lloyd's work, of course, which is assumed to be traditional because its based on traditional songs), but they might as well be for the thousands of people up and down the country who take immense pleasure in gathering together to sing then. It enriches and entertains us, and that living, breathing understanding and appreciation and unleashing of folk music is for many of us overwhelmingly more important in our lives than the narrow academic study of folk music, important though that also is. I suspect when we gather to sing, academic definitions are not - and should not be - at the forefront of our minds.

One song I'd love to see enter the folk scene tradition (as I'll call it to avoid further offence...) is Alasdair Roberts' Farewell Sorrow.