Official estimates of the likely risks associated with long-term exposure to low-level radiation could be out by a factor of 10, a UK panel reports.
Nuclear stations such as Sizewell may have their operations changed
Some divisions marked the work of the Committee Examining Radiation Risks of Internal Emitters and two of its 12 members issued a minority report.
An internal emitter is any radioactive particle retained inside the body.
The findings could prompt changes at nuclear plants and affect the way some medical procedures are undertaken.
Any changes at nuclear power and reprocessing facilities are likely to be operational ones that further restrict the amount of radioactive material that can be released into the environment.
The chairman of the committee, Professor Dudley Goodhead, said the main finding of the report was that we had to be particularly careful in judging the risks of radioactive sources inside the body.
"The uncertainties are real; they cannot be avoided and we must deal with them," he said.
He added that these uncertainties could be reduced through rigorous scientific research that sought to better understand how certain materials behaved in the body, particularly in children.
Although the risks associated with high doses of external radiation are reasonably well known - not least from the gamma and X-ray exposures experienced by atom bomb survivors in Japan - it is sometimes less clear what the consequences are of swallowing or breathing in small quantities of radioactive particles over long timescales.
Some of these radionuclides are "natural" - radioactive lead and polonium are in the rocks and get incorporated into food plants and animals which we then eat.
But the Cerrie initiative was driven by the concern over the presence in the environment of increasing quantities of human-produced materials, such as the plutonium from atomic tests and fuel reprocessing.
In medicine, too, substances like technetium, thallium and iodine are being put into our bodies to image and treat disease.
Cerrie was set up to address whether the models and methods for assessing the radiation risks and doses involved were reliable - and the majority report of the committee found that they were.
However, it said some of the uncertainties involved were wider than previously thought, meaning in some cases we might be exposed to 10 times the risk and in others we may be faced by almost zero risk.
The UK government's radiation adviser, Comare (Committee On Medical Aspects of Radiation in the Environment), said it agreed with most of Cerrie's findings and shared the view that no fundamental change in radiological protection standards was needed.
It also noted that it had reservations about the way the committee was set up and in particular how its composition "was influenced by environmental politics rather than science".
Comare chairman, Professor Bryn Bridges, said it would have been better for an independent science group to work through the evidence presented by "stakeholders" rather than to ask those stakeholders to try to reach a consensus.
"I think they have done their science pretty well," Professor Bridges explained. "I just don't think it was the most cost-effective way of going about it."
In the end, two members of Cerrie - Richard Bramhall, from the UK Low Level Radiation Campaign, and Dr Chris Busby, from Green Audit - refused to back the committee's findings and issued their own minority assessment.
They believe the health effects of man-made radioactivity in the environment have been underestimated by a factor of at least 100 and possibly up to 1,000 times.
They claim the mainstream scientific community has a closed mind on hypotheses that could explain how low-dose radiation could cause disease, such as leukaemia in children.
"The reality is that the committee has surveyed an ocean of ignorance and uncertainty about the fundamental basis of radiation protection," Richard Bramhall said.
He is supported by Michael Meacher, the former environment secretary who set up Cerrie in 2001.
Ahead of Wednesday's official publication of the Cerrie report, the politician said the findings reflected one-sided establishment opinion and did not "accommodate a full and fair representation of all views".
But Cerrie member Pete Roche, an anti-nuclear campaigner and former Greenpeace representative, expressed his satisfaction with the committee's outcome.
"It's a good report," he told BBC News. "It highlights uncertainty and the precautionary principle, which Greenpeace has been pushing, and that means we now have more arguments to restrain the nuclear industry.
"This is likely to come up next when they look to extend the lives of some of the AGRs (Advanced gas-cooled reactors) because as they get older, their emissions go up."