He credited concern among young people for stimulating the change.

"There was a time in the 19th century when it was perfectly acceptable for civilised human beings to think that it was morally acceptable to actually own another human being as a slave," he told MPs.

"Somehow or other in the space of, I suppose, 20 or 30 years, the public perception of that totally transformed. Now there's a huge change in the public perception [of plastic] - and, if you like, in the public perception of moralities. And I suspect that we are right now in the beginning of a big change."

The naturalist also criticised the practice of paying other countries, mainly those in the Far East, to take plastic waste from Britain.

It follows a Telegraph investigation last year that revealed widespread illegal dumping in Malaysia. In May, Yeo Bee Yin, the country's environment minister, singled out the UK for criticism while threatening to return up to 3,000 tons of low-quality plastic to at least 14 countries.

Sir David also warned that failing to tackle climate change would bring great "social unrest" in the form of pressure from immigration, food availability and the availability of cheap travel.

Despite criticising climate change deniers, including "people in power" in the US and Australia, he said environmentalists should not "stamp on" sceptical voices. "From all ages and all points of view, everybody needs to be convinced by this," he said.

Sir David backed the target to cut emissions to net zero by 2050, which the UK has now set in law, saying it was a "tough target", but he hoped it could be achieved.

Asked if he was optimistic about the future, he said: "I feel an obligation. The only way you can get up in the morning is to believe we can do something about it - and I think we can."

He said the growing voice of youngsters on environmental issues was a source of hope, and referring to the young people who had come to the committee hearing to hear him speak, he said: "It's their futures that are in our hands."

By Henry Bodkin
The Daily Telegraph, London