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On Thursday last week, Green Party leader Zack Polanski delivered what he described was an ‘urgent message to the Prime Minister’.

I’ll be honest, I missed it. As, judging by the front pages of the following day’s newspapers, did everyone else. The headlines were dominated by the Jason Arday plagiarism scandal, the prison crisis and a stabbing in London’s West End.

So I went back and had a look. Polanski held a press conference in which he demanded Andy Burnham call a Cobra meeting to deal with the wildfires that had been sweeping across Suffolk, threatening the Sizewell B nuclear power plant. ‘Should fossil fuel companies be earning or making a single penny of profit’ in the midst of such a crisis, he fumed.

But there was just one problem. By that time the fires were under control. Andy Burnham was on holiday. And the news and political agenda had moved on.

Six months ago Polanski was riding high. His party had won a stunning victory in the Gorton and Denton by-election. The Greens had usurped Labour and the Tories in the polls. Senior Labour ministers were discussing whether the collapse of their party’s Left flank meant they were facing extinction.

And he’s blown it. The once-in-a-generation opportunity handed to Zack Polanski to recast British politics in his liberal image has been squandered. And is unlikely to return.

There are multiple reasons for this Green implosion. The most obvious being the departure of Keir Starmer and the arrival of Andy Burnham.

Not long ago, Zack Polanski was riding high after the Greens usurped Labour and the Tories in the polls, writes Dan Hodges, but now Andy Burnham's arrival has caused an implosion...

With a single flash of those willowy eyelashes, and a speech pledging to ‘put the care of people at the heart of everything I do’, our new Prime Minister has made progressive Britain swoon. And left Polanski standing at the bus stop, muttering about the poser in the black T-shirt driving off with his heart-throb in his Ford Capri.

‘Andy’s basically shut down Zack’s space,’ one Burnham aide explained. ‘Our polling shows the Green surge was based primarily on Labour supporters whose priority was the cost of living.

‘Yes, they leaned Left on a number of issues. But that was their prime driver for switching. And Andy’s been able to demonstrate not just that that’s going to be his own priority as Prime Minister, but that he’s got the levers to actually do something about it.’

But there’s more to the Green decline than the Burnham bounce. Since March, the party has been haemorrhaging support at an increasing rate. Partly, this is owing to a chronic inability to set the agenda. Which, in turn, is linked to its decision to move away from its core issue of the environment.

For well over a fortnight the nation’s TV screen were illuminated by the wildfires burning across Europe, then latterly here at home. A fierce debate followed over the causes, and the link to global warming.

But Polanski was completely absent. And by the time he finally reacted, the news bulletins were being dominated by the small-boat crisis and the furore of early releases from jail.

There is another clear reason for the squandering of the Green’s post-Gorton momentum. Polanski has fallen in with a bad crowd. And as a result, his party’s brand has rapidly become toxic.

When Polanski took over as leader, he threw open his doors to a lot of the unsavoury elements that had abandoned – or been turfed out of – Labour after Starmer’s de-Corbynisation purge. And they are now having the same corrosive effect on the Green’s electability.

Since Green MP Hannah Spencer, pictured, won the by-election in Gorton and Denton, Polanski has squandered the Green Party's momentum and support has been haemorrhaging

This was perfectly encapsulated by the recent row over Polanski posting a photo of a Green activist sporting an image of a guillotine with the slogan ‘We’re only making plans for Nigel’ across his social media account. Polanski admitted the image was inappropriate, deleted it and stated it had been posted in error.

Yet he consistently and stubbornly failed to apologise to Nigel Farage – the target of the threat – for his mistake. Why? Because he clearly felt that an apology to the Green’s public enemy number one would see him losing face with his own supporters.

Nor was this an isolated incident. Last month it emerged that the Green leader of Hackney Council, Zoe Garbett, had set a deadline of October 7 – the anniversary of the 2023 terror attacks that saw 1,200 Israelis murdered and 250 taken hostage – for talks to end the twinning arrangement with the Israeli town of Haifa. A council spokesman subsequently claimed the date had been set in error.

But the biggest problem Polanski faces is not Andy Burnham, or his floundering political strategy or his embrace of the flotsam and jetsam of Corbynism. It’s Zack Polanski himself.

The reality is the Great Green Hope hasn’t got it. Massively hyped on social media by his supporters prior to his election, he has been found out. His speeches are laboured and cliched. His policy stances are boil-in-the-bag. His political strategising is childishly simplistic – essentially involving finding an existing progressive position, then moving a stride to the Left of it.

All of which means he is indeed reshaping the political landscape. But not in the way he hoped.

‘The Green threat is melting away,’ one minister told me. ‘And that has big implications for how we move forward.

‘We don’t have to flex as much to the Left as we thought we might have to. It gives us more flexibility over election timing. And it means we don’t have to split time and resources defending two political flanks at the same time.’

It’s also having an impact on the ambitions of some of those blocked from Burnham’s first Cabinet. Until recently, the perception was the Polanski insurgency made a Labour victory in the upcoming London mayoral election unlikely. But the Greens’ poor showing in the recent Manchester mayoral by-election, and their decline nationally, means the capital is now seen as back in play.

‘David Lammy’s planning to go for it,’ one minister revealed to me last week. ‘His calculation is that with Polanski going backwards the door’s opened up for him.’

I’m also told former Housing Secretary Steve Reed is considering throwing his hat in the ring.

A couple of days ago, Polanski was asked if he would identify his most significant achievement since becoming leader of the Greens. ‘I am in no doubt that if we had not won Gorton and Denton, Keir Starmer would not have had the leadership crisis he had,’ he replied.

He’s right. And by hastening the departure of Keir Starmer, and ushering Andy Burnham into Downing Street, he has almost certainly sealed his own fate.