"Brian Peters, he chooses to sing a song about Fish and Chips, He clearly likes the song, I doubt if he worries about whether he thinks it is a folk song..."

Indeed he doesn't. As you suggest, Dick, I plan my set list with light and shade in mind, like any decent performer does. I don't plan my set around the 1954 definition, and neither - as far as I know - does anyone else. Doesn't mean I don't have an idea of what 'traditional' means, though.