The WA Liberal Party's internal polling shows the state government is in a "far worse" position than that shown by published surveys, which point to a Coalition loss on Saturday, and the preference deal with One Nation is to blame.

A source who has seen polling conducted for the WA Liberal Party one week ago said the government was facing a two-party preferred position of 57-43.

This could lead to the Liberal-Nationals Coalition haemorrhaging as many as 20 seats.

The party has already given up hope in several seats including the marginals of Forrestfield, held by Nathan Morton, and Perth, held by Eleni Evangel. But a source familiar with internal tactics said the party was also not expecting to hold the seats of Joondalup, which is held by Jan Norberger with a 10 per cent margin, Jandakot and Kalamunda, currently held by Health Minister John Day with a similar margin.