Today is the last day people can register to vote in the Labour leadership contest. So I’m going to say it: the Green Party has been relatively quiet about Jeremy Corbyn and his momentous surge to become the front-runner. 

Apart from a press release two weeks ago (mainly saying his rise was ‘no surprise’), Greens have been unsure how to respond. Some members have jumped ship and signed up. Others have simply opted to hold tight and see what happens. And maybe it’s ‘no surprise’.

Part of it – indeed, probably most of it – is tactical. Talking up the chances of a potential left-wing Labour leader could hurt the Greens in (at least) the immediate term. According to sources, we’ve lost around 400 members this month alone – no doubt many of whom are going off to vote for Corbyn.

I’ve heard that members have been told by party HQ that if they vote for Corbyn they’ll have to leave the Greens. This is quite possibly incorrect: after all, if you vote through a union, you don’t have to give Labour any money. You just have to lie to the Labour Party by saying you’re not a member of an opposing organisation. Green Party rules on it are, well, slightly unclear to say the least.

It’s a tough position for the Greens to be in. We’re faced with a likely Labour leader who embraces many, if not most, of our policies – a proper living wage, rail renationalisation, nuclear disarmament, opposing war and austerity and so on. Much Green support comes from people – like myself – who left Labour because it was, put simply, not left-wing enough. Labour refused to seriously challenge austerity in the last Parliament. It looks like that might be about to change.

I went to Corbyn’s rally in Camden last week. 2,000 people turned up – over 1,000 in the main hall, hundreds in two full overflow halls and 500 outside (listening to him speak from on top of a fire engine). This is electrifying for the left – it’s hard for anyone to deny.

So the question is – what do we do? The response from the national party – understandably, to an extent – appears to be ‘say nothing’. While privately many senior figures are encouraged by his rise, publicly there has been very little comment. As I say, on the surface, it might make sense. He hasn’t won yet. We shouldn’t talk up other party candidates. And we are the Green Party – we are different, even to Corbyn. But that’s the point.

We are different to Labour, even under Corbyn. He has talked about reopening coal mines. He prevaricates on proportional representation. Labour have a completely different focus, political tradition and internal culture. And as the response from the Parliamentary Labour Party has made very clear – he is not widely supported among MPs.

That is crucial: they will try and tear him down. It takes about a quarter of Labour MPs to express their discontent to trigger another leadership election. There are already calls to postpone or cancel the current ballot. And the Blairites are mounting an ‘Anyone But Corbyn’ (ABC) campaign. We should be on side to resist these attempts to undermine a genuine alternative to austerity politics.

If he doesn’t win, Labour could tear itself apart. The left will be emboldened but without power. The right will use his loss as an excuse to push through changes to make sure people like him don’t come close again. And if he wins, Labour could still tear itself apart. Talk of splits are simmering, most MPs publicly say they won’t serve in his Shadow Cabinet, and coup-discussions will begin from day one. They will try to oust him from the outset. Labour will be in chaos.

The Greens, on the other hand, will not. Not, that is, if we have a coherent position: i.e. that we are comfortable in our own skin, being left-wing. That this does not cause splits. That having a left-wing leader is the norm, not a source of discontent. That we are a properly grassroots, democratic movement party that doesn’t seek to overturn election results if the ‘wrong figure’ gets in. That we believe in participative democracy and a diversity of views – and that we can handle this. As part of a ‘progressive alliance’, we can keep Labour left if he succeeds – and challenge them if they don’t, or if they fail on the environment. As one senior Green has said in private – ‘Corbyn gets ‘social’ – he doesn’t get ‘green”.

At least one Green Party Executive member has broken the silence. The left-wing International Officer of the Greens, Derek Wall – a member of Green Left and a dedicated eco-socialist academic – wrote in the Morning Star at the end of July that:

‘It is my firm belief that when the left wins in one party, that benefits the left in other parties. I have been impressed by Caroline Lucas’s attempt to promote anti-austerity electoral alliances… like many of us on the left, I find his [Corbyn’s] work and the momentum he is gaining hugely inspiring. I would of course urge all of us who are not committed members of other parties to register to vote for Jeremy.’

If Corbyn wins and Labour don’t split, the Greens’ long-held views will be validated. We should put principle before party and support that. We will be stronger for it. The left will be stronger for it.

When one of my best friends recently said he was joining Labour (in part to vote for Corbyn) – after years of trying to get him to join the Greens – my view was this: fair enough. That’s where your fight is. We have our own fight in the Greens. But we are pluralists, and we fight together.

And the Greens and Labour – united, for the first time in decades, around core progressive policies – can win together, too.