Mr Whitely said the reported figure of at least 20 MPs who no longer supported Mr Ripper was "conservative" and he believed there were more.

He called on Mr Ripper to return from holidays and resign, rather than contest the position for the second time in a year.

"I think he should stand down, I don't think he's got the numbers," Mr Whitely said.

"But if not [Mr Ripper does not stand down] we need to get a quick resolution to this."

Mr Whitely said Mr Ripper's position became untenable when last week seven members of the left faction, including deputy leader Roger Cook, publicly revoked their support for him.

"The longer it drags out the worse it is for us," he said.

"[Mr Ripper] needs to read the writing on the wall and step down and declare the position vacant.

"Ultimately if he doesn't step down there will be a contest."

When asked how long the party would allow the issue to linger before forcing a contest, Mr Whitely said "not very long".

The leadership became dogged following consistent poor polling, with the most recent putting Mr Ripper 41 percentage points behind Colin Barnett as preferred premier.

Mr Whitely, who is aggressively non-factional, said Mr Ripper had allowed the factions, particularly the powerful left faction, to flourish to the party's detriment.

"I don't think Eric's a natural leader and I think [the public] sense that," he said.

"Leaders lead. They get up and they say to the factional powerbrokers 'on this occasion you're wrong' and I'm not doing what you want to do.

"I don't think Eric said that often enough and as a consequence I think we've got ourselves into this."

Mr Whitely said the voices of Albany MP Peter Watson, Forrestfield MP Andrew Waddell and Collie-Preston MP Mick Murray - who are all in critically marginal seats and no longer support Mr Ripper - had to be heard.