As far as the time line goes, I am using "Dave Van Ronk The Mayor of McDougall Street" edited by Elijah Wald as a source. Dave credits the folk music happening in the late 50's Donnegan's hit "Rock Island Line" was several years before. Donnegan's only commercial success in the US was "Does the chewing gum loose its flavor on the bedpost overnight" kind of a silly nonsense ditty that had nothing to do with the Leadbelly- Big Bill material he made famous in the UK
I realize the Weavers had hits in the late 40's with "Good Night Irene"
What is significant was that Lonnnie had "working class appeal". It has been postulated that the English working class are not as racist and moralistic as their American counterparts and were able to appreciate Leadbelly and Big Bill Broonzy for that reason. I suppose that is another thread.