The WA Premier says his party's deal with One Nation will likely deliver a "Senate-style" Upper House, in a move that has further strained the state's fragile Liberal-National government alliance.

Key points: One Nation preferences to go to Liberal Party in Lower House, giving the party a "buffer" on seats under threat

One Nation preferences to go to Liberal Party in Lower House, giving the party a "buffer" on seats under threat Liberals will preference One Nation over their old allies the Nationals, in regional Upper House seats

Liberals will preference One Nation over their old allies the Nationals, in regional Upper House seats The WA Nationals have attacked the deal as "desperate", say Royalties for Regions may be threatened

The deal would see Liberal Party preferences flow to One Nation above traditional allies, the Nationals, in regional Upper House seats.

In return, the Liberals would demand One Nation preference the Liberals above Labor in all Lower House seats they are contesting.

Premier Colin Barnett said the move was a pragmatic decision by the Liberal Party.

"If the polls are accurate, it would seem that regardless of any arrangement about preferences, the One Nation Party is likely to win at least some seats in the Upper House," he said.

"I imagine we're going to have a complicated Upper House, regardless of which party wins the overall election.

"We're headed for a Senate-style situation in the Legislative Council."

He said the deal would provide a "buffer" to some Liberal seats under challenge.

One Nation have polled strongly in Western Australia, with the latest Newspoll showing it could attract up to 13 per cent of the primary vote.

However, a recent poll conducted for the Greens suggested voters would punish the Liberal Party if they aligned with One Nation on preferences.

Colin Barnett (L) says the deal was a "pragmatic" decision for the party. ( ABC News: Rebecca Carmody )

WA Labor have ruled out a state-wide preference deal with the right wing Queensland-based party.

Mr Barnett today would not be drawn on the character of One Nation candidates, saying he was satisfied with the deal.

"It is unusual, but it is a practical, pragmatic decision by the Liberal Party, because what we're out to do is to retain government," he said.

"I'm not going to run around criticising or defending candidates from other parties ... my only focus is on the Liberal Party, on maximising our votes in both the Lower House and the Upper House, and doing all I can to defeat the Labor Party."

WA Nationals lash out at 'desperate' deal

Senior WA Nationals MP Colin Holt said he was not surprised by news of the deal, which he described as "desperate".

"I think it could probably be expected, the Liberal Party are only concerned about their political survival," he said.

"They've always focused on metropolitan Perth, the Nationals have kept them honest as a regional party."

The National Party used the balance of power to establish the Royalties for Regions program, which directs 25 cents in the dollar from mining royalties to regional projects, when they won the balance of power in 2008.

Mr Holt flagged concerns the program, which has been wildly popular with country voters, would be lost if the Nationals lost their partnership with the Liberals.

Deal not about helping a party 'over the line'

One Nation's leader in WA, Colin Tincknell, refused to confirm whether a deal had been made.

But Mr Tincknell said he understood why the Liberals would have problems with the Nationals.

"Brendon Grylls was thinking about forming a coalition with a Labor government at one stage — that's something that would've been on the nose with the Liberals, I understand that," he said.

"The mining tax that he's proposed up in the Pilbara is also something that's on the nose.

"We have some problems with the Nationals but we're prepared to sit down and work out a deal with them if they're prepared to sit down with us."

Mr Tincknell said any deal was about helping One Nation win seats, not about helping a major party "get over the line".

"The main thing here is Mark McGowan has refused to deal with us," he said.

"He has to then live by the consequences of his deal. If he refuses to respect us as a party, he will pay the consequences for that."

He said One Nation in WA was still opposed to the sale of Western Power.

Barnett will do anything to win: McGowan

Labor leader Mark McGowan slammed the deal as "desperate and sneaky", and said it reflected badly on the Premier.

"Mr Barnett will do anything to win the next election, this is a recipe for chaos and dysfunction in Western Australia if the Liberal Government is re-elected," he said.

"Western Australia is now on the precipice, this is now the most important election in living memory.

"Understand this all West Australians — if you vote for One Nation, that's a vote for the Liberal Party, if you vote for the Liberal Party, that's a vote for One Nation."