Rowley Powley

As generally inclined to the belief that everything is older than anybody knows of, I am rather startled by "Rowley Powley" not being as old as myself. I remember seeing mentioned somewhere, without any reference to this chorus, that *rowley powley* is a name for a plump fowl, of which both "gammon and spinach" are posthumous connexions. I cannot help thinking that this may be a clue to some prior occurrence of the chorus, with or without the song. If "derry down," which has been said to be druidical, were judged of by the last song it went with, how old would be the Druids?