The Environment Agency said Britain's Atomic Weapons Establishment (AWE), which assembles, maintains and decommissions nuclear warheads, had reported that their site at Burghfield in Berkshire had experienced severe flooding.

"Several parts of the site, including a number of buildings and the site's sewage treatment works, have been affected," the agency said. "AWE staff have been sampling and analysing the floodwater from the site. They have confirmed that there has been no escape of radioactive materials."

Prime Minister Gordon Brown visited the western county of Gloucestershire, badly hit by the flooding, and promised more money to help with drainage and flood defences.

"What we saw here was a month's rainfall in some places in an hour, something that was quite unprecedented, and put enormous pressure on water and the emergency services," he told reporters.

Benn said up to 10,000 homes had been or could be flooded and about 45,000 homes had lost power.