Environment Secretary Hilary Benn has defended the government's response to the floods, as waters continue to rise.
The Army is taking humanitarian aid to Upton-on-Severn in Worcestershire, and RAF helicopters are rescuing people in Tewkesbury, Gloucestershire.
Seven severe flood warnings are still in place and swathes of Warwickshire are also submerged.
Environment Agency chief executive Baroness Young said £1bn a year was needed to prevent future flooding.
She told the BBC that climate change would increase the likelihood of flooding and even with more investment in defences the risk could never be completely eliminated.
Severe warnings are currently in place for Oxfordshire, Berkshire and parts of London, and Tewkesbury is completely cut off.
Mr Benn told the BBC's Sunday AM programme: "This was very, very intense rainfall, with five inches in 24 hours in some areas, even some of the best defences are going to be overwhelmed."
The main developments include:
- Water levels in the River Severn at Gloucester are running at a height of 34ft (10.4m). Flood defences are 35ft (10.7m). Flood water levels are now said to be at the same level as the 1947 floods
- Parts of Worcestershire are under 6ft (1.82m) of water. In Evesham, more than 30 guests and staff are still trapped on the upper floors of the Northwick Hotel
- In Upton-on-Severn, the Army is bringing food and water into the town, which is virtually cut off. Fire crews are also taking food parcels into Worcestershire towns
- Severn Trent Water is warning 350,000 people in the north of Gloucestershire that their water supplies could run out by early on Sunday evening because a treatment plant has been flooded
- Sutton and East Surrey Water has warned 80,000 households and businesses in Sutton to boil tap water before drinking it after the firm discovered rain had leaked into a tank of water which had gone out to customers
- Paramedics took a pregnant woman in her 20s to Cheltenham General Hospital after she became stranded in a car on the flooded M5 near Tewkesbury. She was later released to return home.
- Wide areas of Berkshire are flooded, including 400 homes in Pangbourne where the main road into town is closed.
Meanwhile Mr Benn praised the way the emergency services had dealt with "unprecedented" levels of rainfall and said he had "total confidence" in the response of the Environment Agency.
M5 - reopened northbound between J14, Thornbury and J13, Stroud, after a vehicle fire
A44, A41, A3, A49, A38 - parts closed or blocked
Central Trains - services to and from Birmingham New St, Hereford, Boston and Shirley reduced or suspended
First Great Western - services to and from Paddington, Oxford, Swindon and Gloucester disrupted
Virgin trains - services suspended from Birmingham New St
Chiltern Railways - services from Banbury suspended
Northern Rail - Rotherham Central closed, Sheffield services disrupted
UK airports - no reports of disruption
There had been a cut in the Environment Agency's forward planning budget, but capital expenditure was being increased from £600m to £800m by 2010/11, he said.
Among the lessons to be learned, said Mr Benn, was whether flood defences should be kept closer to vulnerable areas and whether they should be put up earlier - although some may cause unnecessary road closures.
He was responding to criticism flood defences destined for Upton upon Severn in Worcestershire had not reached the town in time because the vehicle carrying them had got stuck in the chaos on the M5.
And he dismissed suggestions that armed forces overstretch meant there were not enough troops available to help deal with the crisis.
Earlier Baroness Young said following Met Office predictions early last week there had been extensive warnings about the floods on radio and television as well as on the Environment Agency website and telephone "floodline" on 0845 988 1188.
Baroness Young urged people to continue checking these sources and to plan how they would cope if forced to evacuate their home. She added that the difficulty had been in dealing with the unprecedented scale of the flooding.
Sir Menzies Campbell, the Liberal Democrat leader, said more needed to be spent on flood defences.
"It was known for some days that this was likely to happen. I think there'll be questions asked about the degree of preparedness there was to meet what is obviously a very, very dramatic outcome," said Sir Menzies.
Conservative leader David Cameron, who has called for a public inquiry into the crisis, visited Witney, the main town in his Oxfordshire constituency, to survey the flooding.
He said people would like to know why flood defence resources were often miles away from where they were needed.
Oxfordshire is preparing for more localised flooding by closing roads and issuing residents with sandbags to protect their homes.
Parts of Worcestershire are under six feet of water
John Parry, of Oxfordshire County Council, said people should "consider moving upstairs, or consider staying with family or friends".
Police have advised anyone travelling through Hereford and Worcestershire to pack supplies and warm clothing as more rain is predicted.
In one of the RAF's biggest peacetime rescue operations around 100 people in Worcestershire were airlifted to safety over the weekend, while more than 1,000 spent a second night in emergency rest centres.
Despite the heightened risk of flooding to central and southern England, the Met Office does not have any severe weather warnings in place.
BBC forecaster Chris Fawkes said parts of the country will experience scattered showers on Sunday, but there will be plenty of sunshine.
There will be also outbreaks of rain across the north east of Scotland, which could lead to heavier bursts.
The Association of British Insurers (ABI) said the final bill for damage and disruption was expected to run into "hundreds of millions".
Kelly Ostler, of the ABI, told the BBC reports of householders not being able to get insurance unless they protected their homes against flooding were inaccurate.
"We have - the industry that is - has a statement of principles with the government that says any home that has insurance at the moment, household and buildings insurance, for flooding and they have maintained flood defences by the government in the area, then they will always have flood cover."
Hereford and Worcester Fire Service, which received more than 2,000 calls and rescued more than 750 people, said by Sunday things had begun to calm down.
Mike Redfern, Assistant Chief Fire Officer in Hereford and Worcester, said: "We've got flood watches, flood alerts, on all the main river systems and we're watching that very closely," adding that the situation was now "fairly well under control".