The outdoor dance floor lies between the brutalist hulk of a defunct industrial building and the murky Thames. “Zionism is racism!” yells the DJ, and a whoop goes up from the Gen Z ravers: women with peroxide hair, men with mullets and fashionable moustaches. “Music is protest!” the DJ continues. “Make some fucking noise!”

This doesn’t look like a typical political meeting, but the thousand or so clubbers gathered in London’s Docklands at the end of May are here in solidarity with the Green Party. Specifically, an organiser says, they came because of Zack Polanski, whose election as the Greens’ leader last year ignited an “explosion of enthusiasm”. Polanski has put the party into British politics by recruiting acolytes in their late teens and early 20s. Above the thudding bass, a 24-year-old called Sophie reels off a list of the Polanski policies she likes: upholding LGBT rights, condemning the “genocide in Palestine”, legalising and regulating all drugs. Maria, who is 26, says he’s “one of the few people telling the truth”. Which is? “Everything is shit right now. We need something different.”

The DJ cuts the music. Phone-cameras are held aloft as Polanski appears at the decks, a trim figure with stubbly cheeks and a T-shirt proclaiming “God save immigration”. “Who is ready for rent controls?” he asks. “Who is ready to tax the rich?” Later he addresses hardcore clubbers in a dark side-room. “Joy is resistance!” he declares. “Community is resistance! Dancing is resistance!” He plainly knows his way around a dance floor, boogying with devotees in a way that, it is fair to say, no other British party leader could pull off. Polanski is 43 but comes across as younger, his Peter Pan demeanour crucial to his success.