Lyrics copied from http://archiver.rootsweb.com/th/read/CORNISH/1999-05/0927646084 and corrected by me. (That web site used the spelling "Trelawney" which is why it was hard to find.) I believe these words now correspond to the recording that was linked to above.

CORNWALL FOREVER
^^
Cornwall forever! We rally at the call.
Cornwall forever! We're coming one and all.
Cornwall forever, and shall Trelawny die?
Here's twenty thousand Cornishmen will know the reason why.
Cornwall forever, and shall Trelawny die?
Here's twenty thousand Cornishmen will know the reason why.

Fish, tin and copper! Make way for Cornishmen.
Fish, tin and copper! Here comes Tre, Pol and Pen.
Fish, tin and copper, and shall Trelawny die?
Here's twenty thousand Cornishmen will know the reason why.
Cornwall forever and shall Trelawny die?
Here's twenty thousand Cornishmen will know the reason why.

* * *

Here's an article about Jonathan Trelawny.