I don’t know where Andy Burnham found his magic lamp, but I hope he’s taking good care of it. In the early hours of Friday morning, the genie that’s looked so kindly on him these past few months granted him yet another wish, with a byelection win in Holborn and St Pancras. It was just the latest gift for a prime minister for whom things keep going right – and who is especially blessed in his choice of opponents.

Let’s start with that win in London, where Labour’s Sagal Abdi-Wali defeated the Green party leader, Zack Polanski. It’s easy to miss how rare such a victory is. As the veteran psephologist Peter Kellner pointed out, this was a win that “defied history”. If the past half-century were any guide, Labour should have lost, thanks to a “truly dreadful record” defending its own seats when in government and facing a byelection challenge from the left or centre-left, the likes of the Greens or the Lib Dems. The average swing against Labour in such contests had been 24%. “On those figures,” wrote Kellner, “Polanski should have won at a canter.” But he lost.

That reinforces the case Burnham made for why he should replace the previous Holborn and St Pancras MP, one Keir Starmer, as Labour leader: namely, that he was uniquely placed to defeat challenges from both left and right. This latest win over the Greens, coupled with his own success in Makerfield in June, is early vindication of that argument.

Burnham can claim much credit for the London result: it’s his leftward shift that has persuaded many progressive voters that they don’t need to vote Green to get what they want and that they should give Labour another chance. But Burnham really ought to share the credit with Polanski himself, who has proved a most generous adversary.

Yes, Polanski brought an initial surge in energy, enthusiasm and membership to the Greens. But under him the party has steadily dismantled the moral halo it once enjoyed as the UK’s foremost advocate for the planet, reshaping itself into something darker. Thanks to Sunday’s........

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