The Greens will be looking for alternative ways of working with the major political parties after this morning confirming any coalition with National is "highly unlikely" at their annual meeting in Auckland.

Co-leader Metiria Turei announced her party's preference to work with Labour but said it could in theory form a coalition government with National.

However she later said National would have to abandon many of its core policies before that happened.

"They've got a very poor policy platform when it comes to dealing with poverty, their attacks on beneficiaries, their subsidisation of polluters, their economic ideas, a lot of their policy around transport. They would have to change."

Nevertheless, the remit agreed to by 200 delegates at the meeting softened slightly, both from the draft version which described the prospect of a coalition with National as "extremely unlikely" and the Greens' previous pre-election stance which ruled it out completely.

Ms Turei said it was more likely that the Greens work "project by project" with National as it has done over the last three years under a "memorandum of understanding".

That had enabled the Greens to negotiate $400 million worth of Green policies including home insulation, pest control, and contaminated site clean up programs.

"We can get stuff done and I can promise more wins with either National or Labour."

She later said the Greens were exploring alternative options to the MOU or more formal confidence and supply agreements including a "constraint agreement".

Constraint agreements, which have yet to be put in place anywhere in the world, are where the smaller party secures undertakings from a larger partner not to go ahead with policies it does not support, rather than securing policy gains.

But co-leader Russel Norman acknowledged the differences between the two parties made a confidence and supply agreement an outside chance at best.

"Unquestionably there's a huge gulf between the Greens and National on social policy and a lot of other policies to be honest."

That gulf was highlighted over the weekend in Dr Norman and Ms Turei's speeches.

Ms Turei attacked Prime Minister John Key's recent announcement that National would campaign on what she said were "vicious recommendations of the Welfare Working Group" such as benefit cuts and linking benefit receipt to contraception.

"National has made vulnerable families into enemies...The Green Party will not be part of this abuse of our families and children, will we?"

Dr Norman criticised both National and Labour of lacking the courage to ensure the largely Australian-owned banking sector acted sufficiently in the best interests of the New Zealand economy in recent years.

He also attacked National's plan to partially privatise state-owned energy companies and both major parties record on key environmental issues including climate change, commercial fresh water use and pollution from dairying.

The Greens' marginally more open stance towards National may be seen as a bid for mainstream acceptance or, as suggested by political blogger and National Party supporter David Farrar, as a bargaining chip in any post election negotiations with Labour.

The Greens were left out of Labour's 2005 coalition government after NZ First leader Winston Peters and United Future's Peter Dunne said they would not work with them.