The prime minister was discussing the challenges facing the natural world with conservation charity WWF UK’s chief executive Tanya Steele.
“I think we need to bring nature back,” she said. “Our planet, 97 per cent of the mass of mammals on this planet is humans and our animals, our domestic animals.
“Just 3 per cent is left for the wild.”
The prime minister responded that it was “so sad” before adding: “We could feed some of the human beings to the animals, that would, that would be...”
Ms Steele jokingly replied: “We could have a vote later and ask if there's any candidates.“
The off-script remark came after Mr Johnson surprised environmental campaigners by claiming recycling plastic “doesn't work”.
During the press conference at No 10 he said: “Recycling isn't the answer. Recycling... it doesn't begin to address the problem.”
Ms Steele said: “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 replied: “It doesn't work.”
Responding to those comments, the Recycling Association said the prime minister had “completely lost the plastic plot”.
Chief executive Simon Ellin told BBC Radio 4's World At One programme: “Wow, I think is the first answer. 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.”
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