Key Points:

National Party leader John Key has floated the possibility of offering the Greens a post in Cabinet if he is in a position to form a government after the next election.

Mr Key today said he did not see big barriers in the two parties working together on environmental issues.

"It's possible. We don't want to pre-judge those things yet. As I've said all along our main goal is to get the maximum party vote we can then look at the details once the votes have been cast," he said on Radio New Zealand.

"If it becomes an environmental debate then I think it's very possible actually National and the Greens could work out some sort of relationship."

However he said an agreement would be more difficult if the Greens' put their social policies, which were quite different from National's, high on their negotiation list.

In almost eight years in Government Labour had delivered little to the Greens, Mr Key said.

He claimed Labour's record on the environment had been poor and National could easily agree to everything the Greens currently had in their agreement with Labour.

"The Greens have been in since 1999 but never have had a Cabinet post," he said.

"They may look back on that period and say for all of the argument about them being closely aligned to Labour, what have they got out of it."

But Prime Minister Helen Clark said an agreement would be difficult as there was little common ground between National and the Greens.

"The Greens generally are a progressive party. Labour is a progressive party. They come at it from a Green perspective, we come at it from a social democratic perspective," she said.

"There is an awful distance from that to a neo-conservative party like the National Party," she said on Radio New Zealand.

Miss Clark said Labour had a strong and close working relationship with the Greens.

The Greens hold their annual conference this weekend, with one of the issues up for discussion being whether it should back Labour going into the next election.

Green Party co-leader Jeanette Fitzsimons said the party had yet to form a position on whether it could work with the new-look National under Mr Key.

"We have no idea whether the new face of National actually has got anything behind it or not," she said.

"There's no policy. He (Mr Key) says carbon trading but we have no idea how he wants to do that and what it would lead to in terms of reducing emissions," Ms Fitzsimons said.

Co-leader Russel Norman said that at the end of the day what mattered was policy "and we've got to base it on that".

He said: "At the moment we think Labour and National are close to each other but at the moment Labour is closer to us than National is."