The way scientists think about their work is changing with the new "precautionary principle" of trying to minimise environmental hazards, according to the chairman of the Royal Commission on Environmental Pollution.

Sir John Houghton, speaking at the Edinburgh International Science Festival, said that the change had emerged from the need to weigh up uncertainties. If there was a perceived environmental problem, the precautionary principle called for action even if scientists could not precisely quantify the hazards.

"Scientists are very conscious of the need not just to do good science, but express what they know and what they don't know in a way science has not done before," Sir John said.

"Six years ago, the majority of scientists would say 'We cannot make guesstimates because there is so much we do not know', but we have begun to realise that we have a real responsibility, and if we don't say what we do know, other people will say it for us," he said.

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Sir John said that both basic and applied academic research underpinned the work of the 25-year-old Royal Commission, which has produced key reports on environmental issues ranging from lead pollution to freshwater quality. "Academic research is absolutely vital," he said. "A lot of our work is based on work going on in universities."

The commission has been stung by criticisms that its report last year on transport attacked private car ownership.

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Commission member Richard Macrory, director of Oxford University's environmental change unit, said that Oxford University Press was to publish a paperback version of the report (which in its present form costs Pounds 25), which Professor Macrory hoped would stimulate public debate and "remove some of the misrepresentations".

He said: "We are not anti-car or anti-lorry, but we want to see an approach to transport that offers more choice."