Only a few months ago, in the spring, there was a sense of giddy possibility about the Greens. Zack Polanski’s radical new leadership felt fresh and dynamic, especially compared with those of the other parties. Former Labour supporters, in particular, were switching to the Greens in huge numbers, Green candidates were winning across the country, and the party was second behind Reform UK in some national polls.

Like Reform, the Green party presented itself as a revolt against a failed status quo. Unlike Reform, the Greens’ urgent stance on the climate crisis gave them a potent moral authority: even many people who did not support them believed that the Greens were right about the most universal issue.

After an unprecedentedly hot summer, some of that authority and momentum remains. Last weekend, at the party’s bustling conference in Brighton, impressive-sounding statistics about the party’s growth this year – along with modern icons of Green success, such as Hannah Spencer, victor of February’s Gorton and Denton byelection – were presented to determinedly cheering delegates in crammed halls.

This week, in the high-profile London constituency of Holborn and St Pancras, where Polanski hopes to succeed Keir Starmer in Thursday’s byelection, the usual cheery squads of Green activists have been striding back and forth between wealthy streets and council estates, distributing thick bundles of a party newspaper with the front-page headline “Greens close in!”. Given the party’s recent election record, Polanski’s populist appeal and the possibility that some of the many local leftwing voters may see the contest as a low-risk way to warn Andy Burnham not to follow Starmer’s premiership rightwards, a Green win is not........

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