Let me be clear. They use the tuning fork all the time (Have they no shame?) What is worse, though, is that they are so brazen about breaking the rules they are quite willing to point it out.

This is obviously a result of the dubious advice they have received from their elders. I have found a dusty report in an old archive by a Sgt. A. Lloyd:

"Though none of the singers can read music, their style of harmonising is not haphazard; it has been arrived at quite consciously by trial and error and rehearsal, and it is characteristic that the Coppers pitch their songs with the help of a tuning-fork. In their very deliberateness, it may be felt, they are departing from folk practice."