An angry Roger Cook has lashed who he calls 'east-coast clowns' over an explosive proposed shake-up of the GST carve-up.

The GST system has become so broken that a bushfire in NSW delivers a financial windfall to the taxpayers of Western Australia.

The Productivity Commission finds the WA GST deal is a "costly mistake" that has led to "perverse" outcomes, and recommends it be scrapped.