The Australian Greens have lobbed a grenade into their New South Wales branch in a dramatic escalation of the more right wing leadership’s long-running campaign to purge the left wing of the party.

The Australian Greens party room, comprising the 10 federal parliamentarians, announced in a statement on 28 June that it has voted to exclude NSW senator Lee Rhiannon from discussions and decisions “on contentious government legislation” until the NSW branch ends “its practice of NSW MPs being bound to vote against the decision of the Australian Greens party room”.

This is a direct ultimatum to the NSW Greens: either get with the increasingly right wing program of Greens leader Richard Di Natale and his backers or piss off.

The immediate issue was Di Natale’s and South Australian senator Sarah Hanson-Young’s desire to stitch up a deal with the Liberals over the “Gonski 2.0” school funding package. They hoped to present themselves as responsible parliamentary operatives, willing to compromise, and in the process secure a few more crumbs for public schools than the government’s initial proposal.

The fact that the deal would still cut billions from school funding compared to Labor’s original policy, while entrenching obscene levels of funding to private schools, didn’t worry them.

In the end, the government didn’t need the Greens’ votes. Di Natale was left to give a pathetic press conference, complaining that despite the Greens’ willingness to help the Liberals, the party had been ever so rudely bypassed.

The Greens leadership then turned its ire on Rhiannon, who had had the temerity to oppose the Gonski 2.0 plan, and whose office endorsed a leaflet, produced by local Greens members, pointing out how much money local schools would lose under the Liberals’ plan.

For Di Natale, former party leader Bob Brown and other proponents of “professionalisation”, the real crime was not the Liberal Party robbing billions from public schools; it was Rhiannon embarrassing the leadership as it attempted to support those cuts.

This episode has exposed the Greens parliamentarians who lined up squarely with Di Natale’s leadership in his attack on the NSW left. Only Victorian MP Adam Bandt voted against excluding Rhiannon from the party room, and only after supporting the more general attack on the NSW branch.

This is just the latest salvo in a longer attempt to destroy the left in the Greens. For a decade at least, the Greens have been repositioning toward the political centre, seeking a seat at the table with the political and media establishment and ditching its “protest politics” image in the hope of greater electoral advance and entry into a future governing coalition.

This doesn’t mean the party can’t ever take a welcome, strident stance – such as the walkout during Pauline Hanson’s racist speech last year. The national leadership’s campaign against Rhiannon is not about completely trashing the social justice image of the Greens, but about establishing some non-negotiables in relation to party policy and practice and sending a message that the Greens is not a place for activist reformers or those wanting to challenge the leadership.

Two key elements of the party’s longer term trajectory into “neoliberals on bikes” (a term coined by critics of the same process in the German Greens) have been a willingness to deal with the Liberals and increasingly vociferous attacks on the left, apparently coordinated with ex-leader Bob Brown.

After the 2016 election, Brown called for Rhiannon’s resignation. “You can’t have people who are still doing things the way we did them in the ’70s and ’80s still in control”, he told the Guardian’s Melissa Davey. “They need to give way to modern young people, including young people in professions like business and law who are keen on changing society for the better.”

Now he has weighed in again, telling the Guardian on 26 June: “I can’t fathom it, ultimately it comes down to a more doctrinaire position which overcomes political good sense”.

The argument is that the NSW branch is unelectable because it is stuck in a loony left time warp and stubbornly and inexplicably refuses to embrace the modern times of cynical pragmatism. The attacks bear an uncanny resemblance to the arguments used for two years by the Blairite right wing of the British Labour Party to try to destroy Jeremy Corbyn’s left wing leadership. It is a similarity the Greens attack dogs seem determinedly unaware of.

Unfortunately, despite Rhiannon’s long history of left wing politics, she is in no position to become the next Jeremy Corbyn. The right is on the move thanks to recent preselection victories over the left within the NSW branch. There is now a clique of four NSW parliamentarians – including the two most recent additions: former intelligence officer Justin Field and business owner Dawn Walker – which is determined to undo the left’s hold.

These preselection contests revealed many weaknesses of the left. Internal divisions, careerism and an unwillingness to confront the right politically characterised those efforts. The left ran several competing candidates, whose campaigns were almost indistinguishable from each other or the right. That was partly due to the left allowing itself to be bound by ridiculous anti-democratic rules that prevented candidates from criticising one another.

Now that the NSW branch has been presented with a stark ultimatum, it has three choices: capitulate and maintain a seat at the table of a pathetic “tree Tory” Greens Party, fight to push back against the right or leave the Greens to form a new left wing party of some sort. It is too early to tell how different sections of the branch will respond.

Rhiannon faces a preselection battle in the next few months, which will be another showdown against the right. She has responded to recent threats of expulsion by reiterating her opposition to the Liberals’ school funding cuts. Rhiannon’s statements rightly point out that she was merely upholding the democratic will of NSW Greens members.

Until now, however, such statements from Rhiannon, and other NSW parliamentarians defending her, have remained entirely defensive – that is, confined to justifying Rhiannon’s actions in this instance but not taking up the broader issues of the appalling right wing stance of nine-tenths of the federal parliamentarians, or what this means for the Greens more generally.

Given the sharp escalation of the attack on the NSW branch, such a defensive response will lead only to a drawn-out defeat. If the left wing of the Greens is to survive, it will do so only by waging a much more open political fight against the right. That would involve going beyond organisational questions of party democracy, important though that is, to combating the accommodation of the party leadership to neoliberalism and extreme moderation.

After all, in a world of ever-expanding inequality and as politics becomes increasingly polarised in country after country, what is the point of a Greens Party that limits itself to the politics of tepid, middle of the road, hand-wringing liberalism combined with a big dose of parliamentary cretinism?