Jonathon Porritt, one of British Prime Minister Gordon Brown's leading environmental advisers, is to warn that Britain must drastically reduce its population if it is to build a sustainable society.
Porritt's call will come at this week's annual conference of the Optimum Population Trust (OPT), of which he is patron.
The trust will release research suggesting the U.K. population must be cut to 30 million if the country wants to feed itself sustainably.
[Britain's population is now about 60 million and growing.]
Porritt said: "Population growth, plus economic growth, is putting the world under terrible pressure.
"Each person in Britain has far more impact on the environment than those in developing countries, so cutting our population is one way to reduce that impact."
Population growth is one of the most politically sensitive environmental problems. The issues it raises, including religion, culture and immigration policy, have proved too toxic for most green groups.