Don Brash will have a clear message for the Act board on Saturday: if his offer of leadership is rejected, his new party will potentially bleed the Act Party dry of any votes it has left.

The former National Party leader has commissioned a nationwide poll to gauge the level of support for him as leader of Act versus Act under incumbent leader Rodney Hide.

Dr Brash expects the results next week, after the Act board meeting on Saturday which he is asking permission to speak at.

"I'd like to say to the board that, under my leadership, I believe Act has a much better prospect of not only getting back into Parliament but having a significant number of MPs."

He will also point out that a new party, which he will set up if his bid to roll Mr Hide fails, could seal Act's fate by taking a bite out of its voting base.

When asked if that could be seen as a threat, Dr Brash said: "I don't want to put it in that way but I am deeply concerned about where the country is and if I can't make a contribution in the Act Party, I'll find some alternative way of doing so."

His preferred approach would be as leader of Act, he said.

"The party's already established, it has a constitution, a membership ... It's got all those things that are easier to take over than to try and create from scratch. I don't doubt I could do it but it would just be much more convenient to assume the leadership of Act."

If successful, Dr Brash wants former Auckland City mayor John Banks to stand in Epsom, which Mr Hide currently holds.

Mr Banks has not ruled that out. He said Epsom and Mr Hide had "parted company". But when asked if he would like to represent Epsom one day, he sidestepped the question saying: "They're a great bunch, the people of Epsom."

Mr Hide has said Dr Brash's bid is a takeover attempt by a member of a different party.

Confident of keeping his leadership, he said if Dr Brash wanted to become leader, he would have to follow the process and first become a member of the party.

Right-wing political commentator Matthew Hooton does not expect Act to take up Dr Brash's offer - even though he believes it is the party's only chance of survival.

"Act is a cult of Rodney Hide acolytes," he said. "I think they'd all prefer to commit political suicide than take this opportunity. And if they don't take it, the new [Brash-led party] will be more successful than Act."

According to the party constitution, the caucus can recommend a new leader by majority.

The board must accept the caucus' choice unless at least eight board members vote to overturn it.

Dr Brash needs three votes from the caucus and the support of at least five board members to block a vote of eight or more against the caucus recommendation.

There are normally 13 board members but the Waikato/Bay of Plenty seat is vacant.