Anti-poverty activist Sue Bradford has revealed she left the Green Party over what she saw as its shift toward right wing politics.

Ms Bradford resigned as a Green MP in September 2009, months after missing out on party's co-leadership to Metiria Turei.

In a post on this afternoon, Ms Bradford said disappointment over losing that vote was not her main reason for leaving the party.

She was instead motivated to go by its business friendly policy increasing openness to working with National.

"My position within the party became untenable in 2009, not just because of the co-leadership vote, but also because I could see clearly that a majority of members preferred a cleaner, greener capitalism to the ecosocialist agenda which I support.

"I refrained from talking about this publicly because it was likely to sound like sour grapes, and because I still harboured hope that perhaps all those good people who remained within the party would see that going down the road of the Irish and German Greens - or the Maori Party - is a recipe for disaster."

The Greens announced on the weekend they may consider working with National.

In a speech to party faithful, Ms Turei said the prospect of a coalition or confidence and supply arrangement with National was "highly unlikely", but did not rule it out.

Ms Bradford said that statement was the end result of a infighting that started in the wake of the sudden death of former Green leader Rod Donald in 2005.

She accused the party of abandoning its radical principles to open itself to relationships with Labour and National.

"The Green Party of Aotearoa New Zealand has now joined the majority of Green Parties around the world who believe that in the struggle to save the planet Greens should support any party in government with whom they can cut good enough deals.

"I accept that this is a democratic decision of party members, just as the co-leadership outcome was, but I cannot help but be saddened by it, and by the loss of the clear, radical social and environmental justice kaupapa for which the party stood when Rod was one of its leaders."