Zack Polanski’s landslide election as leader of the Green party marks a turning point for Britain’s fractured left. Young, rhetorically fluent and unafraid to cloak climate arguments in those about class, Mr Polanski is nothing if not ambitious. He sees his party not as a parliamentary pressure group but as a replacement for Labour itself.

His ascent might have seemed fanciful last July when Labour had just won a thumping majority. Yet Labour languishes in the polls. Sir Keir Starmer’s personal ratings have collapsed. On the extreme right Reform UK now boasts 237,000 members, 870 councillors, and 10 councils under its control. The Greens have more MPs than ever before. And the uneasy leadership team of Jeremy Corbyn and Zara Sultana is preparing to launch a new party to Labour’s left. This is no longer political noise at the margins. This is about the structural failure of leadership at the centre.

Sir Keir’s attempt to anchor Labour as a party of managerialism has created an ideological vacuum. He has offered no

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