It was already known that a high proportion of houses - some 80,000 - in Somerset, Devon, Cornwall, Northamptonshire and Derbyshire had radon concentrations exposing their occupants to a significant risk of lung cancer.
The National Radiological Protection Board survey however, has picked out new areas of risk from Berwick-upon-Tweed, on the England-Scotland border, to Dorset. Three thousand of the homes added to the danger list are in Wales and the rest in England. A Scottish survey has yet to be completed.
Radon is a natural gas which results from the radioactive decay of uranium in rocks. It represents the greatest of all radiation risks to the overall population, outweighing man-made sources like X-rays and nuclear power as well as other natural hazards such as cosmic rays. On average, half the radiation dose we receive each year comes from radon.
Its biggest health impact is as a cause of lung cancers; it is blamed for 2,500 out of 40,000 lung-cancer fatalities a year.
Next month, invitations will be sent to 100,000 English homes in the worst-affected areas offering them a free radon measurement.
But the survey has found there are thousands of homes with radon above the Government's "action level" outside these areas which will receive no notification or free survey.
Windsor falls into a high-radon area, as does Huntingdon - the Prime Minister's constituency - and the Suffolk Coastal constituency of John Gummer, Secretary of State for the Environment. Households here have been excluded because less than 7 per cent of them will have homes above the "action level".
In homes with radon at the action level - 200 Bequerels of radioactivity per cubic metre of air - occupants, if they lived in such a home for their entire life, would face a 1 per cent risk of dying from lung cancer. Radon is much more likely to trigger lung cancers in smokers; their risk would be 10 per cent.
There are means-tested grants enabling low-income families to make these changes in homes with high levels of radon, but these are at the discretion of their council. At most only one-fifth of those householders who do find out they have radon above the action level go ahead and make the alterations, the NRPB says.
The new survey involved taking radon measurements in 250,000 homes, then producing maps based on 5km squares.
Two squares came to light in which more than 30 per cent of homes were likely to have radon above the action level. One straddled Rutland and Melton councils, another is in Staffordshire around Hartington in the Peak District region.
The Government is also going to consult on amending the building regulations, so that new homes in the worst-affected areas have radon-proofing measures built in. (Graphic omitted)Reuse content