Boris Johnson has admitted he is "very worried" about whether the looming COP26 summit will be a success - and warned "it might go wrong".
In a Downing Street press conference with schoolchildren, the Prime Minister said it was "touch and go" whether the global climate gathering in Glasgow achieves its aims.
Mr Johnson appeared to be heavily managing expectations over the summit which kicks off in just six days time.
He said: "We need as many people as possible to go to net zero so that they are not producing too much carbon dioxide by the middle of the century.
"Now, I think it can be done. It's going to be very, very tough, this summit. And I'm very worried, because it might go wrong and we might not get the agreements that we need.
"It's touch and go."
Mr Johnson told the children that meeting the goals of COP26 would be "very, very difficult" but added: "I think it can be done".
He said there would be "peer pressure" on world leaders to act at the summit but warned "it's very, very far from clear that we will get the progress that we need".
Mr Johnson also banged his fist on the table as he insisted that recycling plastic was a "red herring".
He said: "Recycling isn't the answer. Recycling...it doesn't begin to address the problem.
"You can only recycle plastic a couple of times really. What you have got to do is stop the production of plastic, stop the first use of plastic.
"The recycling thing is a red herring."
Appearing alongside Mr Johnson, WWF UK's chief executive Tanya Steele said: "I think we have to reduce, we have to reuse - I do think we need to do a little bit of recycling PM, and have some system to do so."
But Mr Johnson interjected: "It doesn't work. I don't want to be doctrinaire about this.
"If people think we can recycle our way out of problem, we will be making a huge mistake.
"We need to reduce, we need to use far less."
The PM named and shamed Coca-Cola as one of 12 corporations "producing the overwhelming bulk of the world's plastics".
"Big famous drinks companies that you may know but I won't name. I don't know why not, but I won't name them," he said.
"Coca-Cola, for instance, and others, which are responsible for producing huge quantities of plastic, and we've got to move away from that and we've got to find other ways of packaging and selling our stuff."
Simon Ellin, the chief executive of the Recycling Association trade body for independent waste paper processors and their equipment suppliers, said the PM had "lost the plastic plot".
"'Wow', I think is the first answer," he told BBC Radio 4's World at One programme.
"It's very disappointing. I think he has completely lost the plastic plot here, if I'm honest.
"We need to reduce and I would completely agree with him on that, but his own Government has just invested in the resources and waste strategy, which is the most ground-breaking recycling legislation and plan that we've ever seen, with recycling right at the front of it.
"So he seems to be completely conflicting with his own Government's policy."
The Prime Minister's official spokesman said Mr Johnson continues to encourage people to recycle.
"Yes, the Prime minister was setting out that recycling alone is not the answer," the spokesman said.
"We're taking a wide range of action across society to cut plastic pollution.
"Simply relying on recycling alone, as the Prime Minister set out, would be a red herring - we need to go further and take wider action."
Mr Johnson also made a series of bizarre suggestions on battling climate change, including municipal toothpaste dispensers, feeding people to animals to rebalance nature and encouraging cows to stop burping.
