Boris Johnson has admitted Britain could fail to broker adequate enough deals to curb irreversible and devastating climate change at the global summit of world leaders beginning in Scotland later this month.

The prime minister said it was “touch and go” whether the Cop26 event would be a success, as he told businesses it was their job to significantly reduce the amount of single-use plastic they produce and described placing too much responsibility on people to recycle as a “red herring”.

In a question and answer session with several dozen children in Downing Street on Monday, Johnson was hesitant about the degree to which the fortnight-long talks would yield enough commitments to reach carbon net zero output by 2050.

“I think it can be done,” he said. “It’s going to be very, very tough this summit, and I’m very worried because it might go wrong. We might not get the agreements that we need. It’s touch and go, it’s very, very difficult … It’s very far from clear that we’ll get the progress that we need.”

Johnson said it was a “very fair criticism of the world” when challenged by a child on why political leaders were not treating climate change as urgently as Covid. He added: “I share your alarm about where we need to be.”

Government insiders are already fearful about how much progress can be made at the summit, given concern that Russia’s Vladimir Putin and China’s Xi Jinping – whose countries’ economies are viewed as an important part of any global decarbonisation strategy – will not attend the summit in Glasgow.

Johnson named and shamed Coca-Cola as being one of 12 corporations “producing the overwhelming bulk of the world’s plastics”. He said the production of the material for single-use items was a “massive problem” and that businesses should “find other ways of packaging and selling our stuff” such as using seaweed, banana leaves and coconuts as substitute materials instead.

“Recycling isn’t the answer, I’ve got to be honest with you,” the prime minister said. “You’re not going to like this: it doesn’t begin to address the problem. You can only recycle plastic a couple of times, really. What you’ve got to do is stop the production of plastic. Stop the first use of plastic. The recycling thing is a red herring … We’ve all got to cut down on our use of plastic.”

The comment prompted shock from Simon Ellin, the chief executive of the Recycling Association, who told BBC Radio 4’s World at One programme it was “very disappointing” and that Johnson had “completely lost the plastic plot”. He said he agreed plastic production should be reduced but insisted “we can’t get away” from needing it for containing and protecting food. Ellin said a strategy for tackling waste recently published by the government put recycling “right at the front of it”, so Johnson “seems to be completely contradicting his own government’s policy”.

Tanya Steele, the chief executive of the World Wide Fund for Nature, who was fielding questions with Johnson at the event, appeared to take a different view from Johnson. “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,” she said.

Johnson interjected to say: “It doesn’t work. I don’t want to be doctrinaire about this, but if people think we can just recycle our way out of the problem, we’ll be making a huge mistake.”

During the session, the prime minister also cracked a joke in response to Steele saying humans and domestic animals make up 97% of mammals on the planet, leaving stretched resources for wild animals.

Johnson said that to rebalance nature “we could feed some of the human beings to the animals”. He also joked that given cows emit so much methane, “we have to encourage them to stop burping”.