Couldn't disagree more GUEST,Reverend Bayes, Paul McCartney, or more to the point Brian Epstein and George Martin, knew how to shift albums better than almost anybody, no doubt of that. They made a great deal of money out of doing precisely that. But that in itself does not make Paul McCartney "musically important" as I think he was described in the OP. And if a song is not a folk song why would it ever be sung in a folk club?

As someone else brought the subject up, I would love to know what songs Cyril Tawney wrote that weren't folk songs (i.e. Songs written about a typical sailors work and life ashore and afloat). If he did make money from songs such as "Grey Funnel Line" that was because it just happened to be a very good song, with a very good melody that was very popular. It was as much of a folk song as MacColl's "Shoals of Herring" was, all the songs written by Tawney were written with first hand knowledge of what his songs were all about (That's what made them good).