The radioactive fallout from a nuclear accident that rocked Britain 50 years ago was underestimated, scientists say.
In 1957, a fire at the Windscale nuclear reactor in Cumbria led to a release of radioactive material that spread across the UK and Europe.
But new research claims the incident generated twice as much radioactive material and could have caused more cancers than was previously thought.
The research was published in the journal Atmospheric Environment.
The Windscale site was home to Britain's first two nuclear reactors - the Windscale Piles - which were constructed to produce plutonium and other materials for the UK's nuclear weapons programme.
But the rush to build them when little was known about nuclear reactors led to what was at the time the world's biggest nuclear disaster, although it was later dwarfed by Chernobyl and Three Mile Island.
On 10 October 1957, a failure to properly control the temperature of the graphite moderator within the Windscale No 1 pile sparked a devastating fire, which caused radioactive contamination to spew into the atmosphere.
The fire was eventually put out by restricting the air flow, and with water - a risky act which could have caused an explosion - but a radioactive cloud was already spreading far and wide.
At the time of the accident the levels and spread of the radioactive materials was estimated, and measures were put in place to limit radioactive contamination.
But a new study carried out by John Garland, formerly of the UK Atomic Energy Authority, and Richard Wakeford, a visiting professor at the University of Manchester, suggests the contamination of the environment may have been much higher.
The team carried out a re-analysis of data taken from environmental monitoring of air, grass and vegetation and combined this with computer models that revealed how the radioactive cloud would have spread from the reactor with the meteorological conditions at that time.
They confirmed radioactive iodine and caesium were released, as well as polonium and a very small amount of plutonium, but found that the levels would have been higher than previously thought.
John Garland said: "The reassessments showed that there was roughly twice the amount than was initially assessed."
This would have also impacted the numbers of cancers that the accident would have caused, said the authors.
Previously, it was thought that the radiation would have eventually led to about 200 cases of cancer, but the new contamination figures suggest it could have caused about 240.
The researchers said most of the radioactive materials released had now decayed and posed no ongoing risk, but small quantities of caesium and plutonium remained.
Paul Howarth, director of research at the Dalton Nuclear Institute at Manchester University, said a repeat of the Windscale incident would not happen today because the design of modern nuclear reactors was completely different.