Frank:

Presumably you are talking about Sharp's collecting in America. I rather doubt that he ever used the term 'bowdlerised' in relation to any musical instrument; and he certainly didn't say that the banjo wasn't 'a folk instrument'; neither did he ignore it. The diaries he kept during his Appalachian trip clearly show that he heard the banjo being played on a number of occasions. He heard it used for dance music, however, not for song accompaniment. Neither did he despise the instrument, as is sometimes suggested by people who perhaps want him to have; as it happens, he taught himself to play the banjo (though probably not the 5-string form; I'd guess at the tenor, which was popular in England at the time) during one of his recurrent bouts of illness.

I'm not at all sure what all that has to do with any discussion of English (as opposed to American) singing styles, mind.