As Snuffy says the line is Tre Pol and Pen
The full chorus being
For 'tis fish and tin and copper, boys, Tre Pol and Pen And One and All, we may rejoice That we are Cornishmen.
I've lent someone the book that I think it's in. "Songs the Cornish Love to sing" by Mike O'Connor.
A link to his place can be found here. http://www.angelfire.com/mo/kernowfolk/latestlinks.html.
KJ