New South Wales MP Jeremy Buckingham has quit the Greens party and says he will contest the next election as an independent.

The rogue MP announced he was “ripping up” his membership at a press conference on Thursday, after the party formally asked him to step aside as a candidate for the state election in March.

Describing the party as “toxic”, Buckingham said the Greens had “abandoned the core principles they were founded on” and were more focused on “bringing down capitalism” and “divisive identity politics” than acting on climate change.

“The NSW Greens are no longer focused on the environment,” he said. “They are no longer the party that Bob Brown founded and I in good conscience can no longer be a member of that party.”

Describing himself as “one of the best environmental campaigners in Australia”, Buckingham said he would run as an independent for the upper house in March and was in discussions with other Greens members and progressives to run on his ticket.

Buckingham’s decision to quit the party is the culmination of a months long civil war within the NSW Greens.

A former party aide, Ella Buckland, complained to the Greens in April about an alleged incident involving Buckingham that occurred in 2011.

It led to the Greens MP for Newtown, Jenny Leong, using parliamentary privilege to accuse Buckingham of committing an “act of sexual violence” against Buckland, and calling on him to resign.

Buckingham has denied the allegations and pointed to an independent investigation that found there was insufficient evidence to substantiate the Buckland complaint.

Following Leong’s speech the party’s federal leader, Richard Di Natale, called on Buckingham to quit the party.

The intense internal fight led two other MPs – Justin Field and Cate Faehrmann – to threaten to quit the party.

Buckingham took a swipe at Leong on Thursday, saying he would consider teaming up with an independent looking to run in her seat of Newtown.

“I think it’s an interesting electorate,” he said. “A lot of progressive voters there and they might like to hear something from a progressive independent candidate.”

He said that if he was re-elected he would be a “pragmatic, principled MP” focused on action on climate change “rather than my first step being to bring down capitalism”.

“We need to phase out fossil fuels. Coal. No ifs, no buts. We live in a mixed-market economy. We’ve got to accept that.”

Following his announcement Faehrmann put out a statement supporting Buckingham, a sign the internal woes won’t disappear overnight.

“Jeremy is a formidable campaigner on climate change who took on the coal and gas industry like no other MP has ever done,” she said.

“Jeremy should never have had to resign from the party in this way, and I share many members’ concerns at how he has been treated. The fair thing to do now is a recount of the upper house ticket to ensure those members who voted for him aren’t disenfranchised.”