Jim's post at 9-41 and Nick's at 10-53 cover the problem of what is acceptable as a traditional folk song and what is not. as Nick says we know the buttercup song was music hall song but it was known and sung by
two generations of traditional singers. I sing it having learnt it from singers on Dartmoor, I doubt if they knew its source any more than I did for many years. Both they and I sing it because we like it and so do our listeners. The idea that a folk song is pure only if it comes from the ordinary people is true in the very strictess sense. If a song is adopted by ordinary people and passed on to following generations itis still a part of that community so is it an honoury folk song,possibly.