Thousands of homes could be without tap water for up to two weeks, police said today, as the flooding in parts of Britain was described as the worst in modern history.
Gordon Brown accepted that more money needed to be spent on defence work. The environment secretary, Hilary Benn, announced a review headed by an "independent person" and said the "emergency was far from over".
The Environment Agency issued nine severe flood warnings and said the flooding would spread as runoff from Friday's torrential rainfall reached rivers in southern England.
Severe flooding has affected the Atomic Weapons Establishment (AWE) at Burghfield in Berkshire, which is responsible for the final assembly of nuclear warheads. "Several parts of the site, including a number of buildings and the site's sewage treatment works, have been affected," the Environment Agency said in a statement.
"AWE staff have been sampling and analysing the floodwater from the site. They have confirmed that there has been no escape of radioactive materials from the site."
AWE is required to continue with extensive sampling and monitoring of the floodwaters, reporting all results to the agency.
David Griffiths, the team leader of the agency's nuclear regulation group, said flooding had affected the site for three days and he would be demanding that AWE reassesses its flood defences.
An AWE spokesman, Alan Price, confirmed there had been flooding at both the Burghfield and Aldermaston sites during heavy rainfall on Friday which affected "one or two" buildings. He refused to say which buildings were affected, and said there was no current flooding at either site.
The RAF said the flooding of the past few days had resulted in its largest ever peacetime operation.
Homes and businesses near the river Severn have been particularly affected, while the water level in the Thames was rising. Severn Trent Water confirmed that 350,000 homes would be cut off from mains supplies by the end of today.
Oxford and Reading were likely to be flooded in the next 48 hours, the Environment Agency said.
More than 48,000 homes in Gloucester were without electricity after waters entered the Castlemeads substation, which provides power to half the city. Another 70,000 houses were without tap water after the flooded Mythe treatment plant was shut down.
"The best-case scenario is that it will be seven days before Mythe is working, and it may be 14 days before it is fully operational," said Tim Brain, the Gloucestershire police chief constable, at a press conference.
He said emergency flood defences around Walham substation, which provides power for 500,000 people, were "holding for the time being".
"The situation is unprecedented. There are high levels of water and there is more to come. We have by no means passed the peak."
More than 250 bowser tanks were dispensing water to homes cut off from mains supplies in the Gloucester area. Local supermarkets were giving out 150,000 litres of bottled water.
Shona Arora, the director of Gloucestershire public health, said there was a small risk of infection from the floodwaters and advised parents to keep their children away. Water from bowsers should be boiled as a precaution, she said.
Environment Agency spokesman Anthony Perry said: "We have not seen flooding of this magnitude before. The benchmark was 1947 and this has already exceeded it."
Terry Standing, chief officer of Gloucestershire fire and rescue, said the situation across the county remained "critical".
"We have had about 2,500 calls during this crisis - to put that in context we normally have 8,000 a year," he said.
Hundreds of people, including many in care homes, have been airlifted to safety by the RAF. In Oxford, Kassam stadium, on the outskirts of the city, was being used as a temporary shelter for up to 1,500 people.
A council spokesman said: "We have currently got 50 elderly people here. We are waiting to see if there will be any further evacuations from Oxford, Abingdon and the south of the county. If there are, they will all come here."
Around 150 firefighters and servicemen from RAF Innsworth were trying to protect electricity substations north of Gloucester supplying power to 500,000 homes.
West Mercia police said people forced to abandon their cars in south Worcestershire faced having them broken into by opportunist thieves.
The government and emergency services have been criticised for their slow response. The environment secretary, Hilary Benn, told GMTV today that the government had doubled investment for future flood defence over the last 10 years.
"We've seen unprecedented levels of rainfall and flooding that people haven't seen for 60 years," he said.
"The trouble is, when you get that amount of rain in that concentrated a time, even the best flood defences in the world are going to be overtopped, and that's what we've seen in many places."