For more than a decade, Britain’s acrimonious politics has included a fundamental but often misunderstood battle. Sometimes it is fought out in the open and sometimes more in the shadows. Its protagonists extend far beyond Westminster, into the media, big business, the civil service, activist movements and important but neglected parts of the electorate. And despite how long the battle has been going on, it’s still hard to say which side will prevail.

On one side are millions of left-leaning Britons – many of them young – whose economic prospects are worsening, whose anxieties about the climate crisis are rising, whose horror at Israel and the US’s wars is absolute, and whose alienation from the compromises of conventional Labour politics is deep. This is the large minority of the electorate attracted by Jeremy Corbyn’s attempt to radicalise Labour between 2015 and 2019, and now increasingly drawn to Zack Polanski’s leftwing, populist reshaping of the Greens. For both leaders, the ultimate, hugely ambitious aim was or is to create a much more equal, environmentally sustainable country with a much more ethical foreign policy.

Yet fundamentally opposed to this project is another coalition of interests, including the rightwing media, the right of the Labour party, the Conservative party, corporate lobbyists, defenders of Israel and the Anglo-American “special relationship”, and supposedly realistic centrists from the opinion pages of the Financial Times to the deep-state recesses of Whitehall. Protecting Britain’s status quo, by any means necessary, against the disruptive plans of the left has been one of this loose and adaptable establishment’s main priorities for decades, arguably for centuries. And it has rarely been defeated in this struggle.

Thus, Corbyn’s leadership was steadily undermined by claims that he was a dangerous extremist who threatened national security and economic prosperity and tolerated antisemitism, terrorism and Muslim sectarianism. A lifelong anti-racist, peace campaigner and assiduously inclusive constituency MP ended up being seen by too many voters as a promoter of division and prejudice.

Polanski is, in some ways, a very different leader: younger, less set in his ways and a better communicator. The Greens are less weighed down than the Labour left by negative perceptions. Yet it’s striking that only about eight months into his leadership, Polanski’s party is already accused of many of the same political crimes as Corbyn’s Labour. “The Green party is mad, bad and dangerous,” warned the Spectator recently. The rightwing magazine cited the party’s “outlandish proposals … endemic antisemitism … cynical focus on Palestine in order to attract students and voters who don’t speak English … [and] profound economic illiteracy”.

In this context, Polanski’s controversial initial response to the attacks in Golders Green in north London, and his party’s alleged slowness to deal with a small number of its candidates for this week’s elections who are accused of making antisemitic comments, risk creating the worst crisis of his young leadership. Despite having apologised for sharing a social media post criticising the police operation in Golders Green, and despite himself being a victim of antisemitism – serious enough, he said on Sunday, to have led to recent arrests – Polanski is accused by Labour of being “not fit to lead any political party”. It echoes the charge made repeatedly against Corbyn, that he was “not fit to be prime minister”. New data from More in Common shows that Polanski’s approval rating has fallen sharply.

The fact that the Greens are attracting many ex-Corbynistas – from thousands of former Labour voters and members to quite well-known figures such as the activist Michael Chessum, the economist James Meadway and Labour’s ex-general secretary Jennie Formby – could, theoretically, make avoiding a repeat of Corbynism’s demise easier. Such veterans gained a painful understanding of the forces that any British leftwing party is up against – and how, and how not, to combat them.

Alternatively, the Corbyn-Polanski connection and the current antisemitism controversy could mean the Greens lose their useful previous image as the herbivores of British politics, ideologically ambiguous enough to appeal to both urban radicals and rural conservatives. Although the Greens don’t suffer from the entrenched factionalism that so hampered Corbyn’s leadership, such as the enmity towards the left from much of Labour’s bureaucracy and parliamentary party, a few longstanding Green members are beginning to grumble about their party being taken over by “militants”. Such fears, justified or not, have been weaponised by rightwing journalists for as long as reforming British parties have existed.

Polanski himself, a former Liberal Democrat who once heckled Corbyn in public, is now a critical admirer of his Labour tenure, and also a keen student of the rise and fall of other influential British leftwingers, such as Tony Benn. One of the lessons Polanski has learned from Benn is that would-be reformers of our hierarchical economy and society should always challenge, politely but firmly, the conservative assumptions behind the mainstream media’s questions about the difficulty and desirability of transforming the country. Pushing back in this way, without sounding too argumentative or over-elaborate, requires pithiness, awareness of your audience and public confidence. Polanski has those qualities, but a lot more Green candidates will need them, too, if the party is to turn its poll momentum into meaningful electoral success.

The Greens will also need to be better than Corbyn’s party at the politics of attack. While he was damagingly caricatured by the right as on the side of Russia, he failed to highlight the Tories’ then reliance on Russian donors. Today, the Greens need to draw the political conversation away from their own flaws and misjudgments, and back to the social, economic and environmental crises caused by the capitalism with which most of the other parties are entwined.

Polanski and his strategists could also learn from the failure of Corbyn’s Labour to build enough alliances. With chaotic results likely in this week’s elections, the Greens may get a chance to run many more councils – if they are able to share power with other progressive politicians. After the next general election, such alliances may be the only way to keep Reform out of national office. Polanski has said cautiously positive things about relative Labour radicals such as Andy Burnham. But actually collaborating with a wounded, diminished Labour, which many Greens have recently abandoned, would be a great psychological and political challenge for both parties.

Yet unless Polanski’s party finds ways to outperform and outlast Labour under Corbyn – which, for all its flaws, was a highly significant and often vibrant project – the frustrated millions of British leftists may be stuck on the margins of our politics for decades more. Meanwhile, the other large and angry minority, on the right, represented by Reform, may get their chance.

• Andy Beckett is a Guardian columnist
  

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