“The mass extinction of animals and plants being principally driven by our food system, where is that?

“What about the public health dimension, in terms of the people suffering from diet-related illnesses that’s costing countries absolute fortunes on their public health services?

“This is a deficiency in the way we do economics, insofar as we can’t see the downsides of things which are basically hidden from the numbers that appear in the prices.”

Water companies and the Government have been criticised in recent weeks for failing to upgrade Britain’s Victorian water system over several decades, leading to thousands of litres of untreated sewage being dumped in UK rivers and the sea each year.

Under pressure from campaigners and the public, the Government placed a duty on water companies to reduce the negative impacts from sewage dumps in the Environment Act, passed last week.

But fixing Britain’s water infrastructure is likely to cost millions and water companies have called on regulator Ofwat to allow it to raise consumer bills to pay for upgrades.

Putting a price on nature

Campaigners say the companies should instead cut shareholder payouts to fund the changes.

Mr Juniper said he believed the public “are willing to pay some more” if it means having cleaner rivers.

“The people who are paying the bills are also the same people who want to go swimming in the river and to take their kids paddling and go pond-dipping and everything else,” he said.

“A multimillionaire filling up a swimming pool” should pay a higher unit cost than someone with much lower water consumption, he added.

In February this year, a Treasury-commissioned report led by Cambridge academic Professor Sir Partha Dasgupta suggested putting a price on nature to encourage countries to manage it more responsibly.

This could include paying countries to look after forests and charging rent for fishing in communal oceans, the report suggested.