The distinction has to come from your area. Of course it has earlier so-called "Celtic" influences but if the folk musician has spent enough time in a given area, they will take on unique musical and lyric expression. The goal is to study the music in that given area
and learn to play and sing it. Then you will find its unique qualities.

I don't know much about early English folk music but I see that some of it informs American folk songs (as Sharp and Karpeles have shown). I think that American ballads identification with Britain might be overstated but nonetheless, Barbara Allen seems to have crossed the pond with definable strings (no pun intended). My inclination is that most fiddle music is Scots-Irish in the Appalachians and not too influenced by English music.

I think that there certainly are examples of Cornish folk songs, North Country songs,
and probably predecessors in the time of Shakespeare or Henry the VIII. Early sea chanteys may have English origins. The tradition can be defined when isolating the region whereby the unique styles emerge.

Frank Hamilton