It is surely time for the Green party to formally join forces with Labour. Sounds like an absurd proposition? It would unite the English and Welsh left under one banner, bring one of the country’s most inspiring politicians into the spotlight, and reinvigorate the cause to save the planet from environmental destruction. It’s exactly the arrangement that has existed between Labour and the Co-operative party for nine decades: indeed, there are 38 MPs who belong to both. Rather than proving the death of green politics, such a pact would give it new life.

At the last election, the Green party commendably stood down candidates across the country to avoid splitting the left-of-centre vote. With this act of political sacrifice, they did their bit in depriving the Tories of a majority. Our electoral system compelled them to do so, and that is unlikely to change for a long time. In the political era before 2015 the Greens functioned as a leftwing alternative to Labour; but the ascent of Corbynism has rather dented that purpose. Truthfully, the Green party’s prospects are poor.

We live in an era of political polarisation in which the combined share of the two major parties is back to where it was in 1970. All minor parties face the squeeze. In the next general election, the Greens will face the same dilemma: either put forward candidates in key Labour-Tory marginal seats, wave the flag for their own politics but win a derisory share of the vote and potentially allow the Tories to sneak through the middle, or again stand down candidates en masse. Caroline Lucas will remain a campaigning political force in Brighton – but the party’s only MP.

What if – as Momentum founder Jon Lansman suggested back in 2016 – such a pact was made? As with the Co-op party, it would be possible to remain a member of both Labour and the Greens. Full democratic rights would be granted, including the right to select candidates. As we have Labour/Co-op MPs today, there would be Labour/Green MPs too. That would certainly mean significantly more Green MPs than would ever be elected under the current electoral system. It would boost climate change as a political priority. It could also mean Lucas in the shadow cabinet – and later in government – with the environment brief.

It is hardly controversial to point out that Corbyn is closer to Lucas politically than he is to many of his own MPs

This would end a pointless division on the British left. Looking back, the so-called “Green surge” three years ago foreshadowed the rise of Corbynism. The party reached 11% in the polls at one point, and its membership trebled from 20,000 in October 2014 to more than 60,000 seven months later. A woeful 2015 general election campaign by the embattled leader Natalie Bennett drastically undermined the party’s prospects, but it still amassed more than a million votes. Its appeal was particularly strong among younger people who felt disillusioned with Labour’s lack of radicalism – indeed many of those members and voters defected to Corbyn’s Labour party. No wonder: for those attracted to the Green message of a “peaceful political revolution” to end austerity, Corbynism seemed like a natural new home.

Lucas herself has been a committed fighter for causes that must be central to Labour’s message. She was right to criticise pre-2015 Labour for failing to challenge the “austerity message”, and has opposed cuts to everything from women’s refuges to schools. Her courage in fighting climate change led to her arrest at an anti-fracking protest in 2013.In many ways, her campaigning zeal echoes that of Corbyn, who she has repeatedly fought alongside. Indeed, it is hardly controversial to point out that Corbyn is closer to Lucas politically than he is to many of his own MPs, and yet absurdly Lucas is a political opponent.

Yes, the Green leadership wants Labour to go further – on everything from committing to a shorter working week to more radical taxation. But as someone who agrees with her – that Labour’s offer is not yet radical enough – I believe the Greens’ influence in pushing for greater radicalism would be strengthened, not diluted, in a formal pact.

The obstacles to such a pact are sizeable. Some within Labour – and not just on the right – are deeply hostile to the Green party, regarding it as an eccentric, politically inconsistent movement of bourgeois, bohemian eccentrics. And it is certainly true that the Greens have a deeply reactionary faction: some are far closer to the Liberal Democrats in political outlook than they are to socialism. Indeed, some Greens are hostile to the trade union movement, considering it to be as much of a vested interest as big business, rather than the organised expression of the working class. Back in 2013 Brighton’s Green council promoted a disastrous reform that would have slashed some bin workers’ pay by £4,000: local Greens compared the ensuing strike to the winter of discontent . Any seasoned political campaigner will tell you of Green voters who are profoundly anti-Labour, and not for progressive reasons. But there are many thousands of Green activists committed to social justice, workers’ rights, tax reform and a peaceful foreign policy – and they could play a decisive role in electing a transformative government.

A red-green alliance is surely overdue. Although Labour currently presents a radical offer on climate change, such a pact would amplify the measures needed to stave off what is, after all, an existential threat to humanity. The Greens suggest that being separate from Labour maximises their leverage over the party to be more radical. I’m not so sure: it leaves them with a single MP and unable to politically advance. Allied to Labour, they could present themselves as one of a governing party’s radical flanks, and get candidates selected with their politics. This proposal will undoubtedly go down like a cup of cold sick for activists on both sides of the divide. But this could be the makings of a formidable political alliance to defeat Toryism and form a government to both eradicate social injustice and help save the planet. And surely that prize makes the pain of overcoming partisan differences worthwhile.

• Owen Jones is a Guardian columnist