Judith Collins sets her own sacking point: 35 per cent in the polls

National Party leadership contender Judith Collins has set herself a performance threshold of 35 per cent in the polls if she wins the leadership.

And she has also promised a review of all National's policies, including questioning one of its key promises of 2017: tax cuts.

National is still polling at about 44.5 per cent and a new leader's job will be trying to hold that.

She said Labour had shown what the tipping point was before a leader ran into trouble.

"Once things start getting under 35 per cent people start saying 'can we win?' And I know I am putting a mark up there which at some stage in the future, if I am successful this time, that people will say 'well, you set that mark.

"Yep, let me set that mark."

Collins said she did not necessarily believe tax cuts were a priority.

National had campaigned on its Family Incomes Package which included tax cuts from mid-2018 and signalled a further round in 2020.

"I don't know that that is the biggest thing people want, actually. I think people want some very sensible expenditure, but better than that, outcomes in some of the areas they are missing out on."

While her rivals Amy Adams and Simon Bridges declined to talk about policies or the direction they believed National should go, Collins signalled she would review many of National's policies.

"I think it's always good to review all policies when you become the leader."

Collins said the caucus unity any new leader would get would depend on the polls.

"What you do is you show by results. If you can deliver in the polls, then you can deliver for that particular caucus. And if you deliver, strangely enough you get there."

Collins also believed she would be able to do better than Bill English would have done in 2020. She said he had good attributes and she did not want to denigrate his legacy.

"But I do know, coming into Opposition, I know how tough it is. And I know you need a decisive and strong leader. And I also know you need to be able to reach out to other parties."