Thousands of homes along the River Thames have been told to prepare for "significant flooding", as the number of severe flood warnings in the south of England swelled to 16.
Of the severe flood warnings, 14 relate to a lengthy stretch of the Thames through Oxfordshire and Surrey, and two remain in place in crisis-hit Somerset Levels.
The Environment Agency said the Thames warnings stretched "from Datchet to Shepperton Green, including Ham Court and Chertsey, as river levels in the area are extremely high and are forecast to continue to rise".
Communities Secretary Eric Pickles said the areas are expected to suffer "significant" problems by the middle of the week.
Although southern England and Wales will see a quieter day with light showers, the latest storm will arrive this evening with heavy rain of up to 0.78ins (20mm), weather forecasters MeteoGroup said.
While emergency work to prevent flooding continues - including the distribution of tens of thousands more sandbags by the Royal Marines - the Environment Agency boss has hit back at Government critics.
Under-fire Lord Smith has accused ministers of "getting in the way" of vital work to deal with devastating floods by turning the crisis into a political row.
The peer defended the quango's handling of the situation and issued a furious broadside at what he said were attempts by politicians to undermine the work and reputation of the Agency in a bid to secure better media coverage.
"What really saddens me, though, is seeing the Environment Agency's work and expertise in flood-risk management,
internationally respected and locally praised in many parts of the country, being used as a political football for a good media story," he wrote in an article for the Guardian.
"In a lifetime in public life, I've never seen the same sort of storm of background briefing, personal sniping and media frenzy getting in the way of decent people doing a valiant job trying to cope with unprecedented natural forces.
"Our staff have worked their hearts out in order to protect as many people as possible in the face of extreme weather.
"They'll carry on doing so. But there's no place for playing politics in the serious business of flood protection."
Repeated calls for dredging were made to Downing Street and other Whitehall departments by farmers and others in the Somerset region from at least six months ago but funding was declined.
Mr Pickles has blamed faulty Agency advice for the scale of the damage to the Somerset Levels and declined to dismiss calls for the former Labour cabinet minister to resign.
"We made a mistake, there's no doubt about that and we perhaps relied too much on the Environment Agency's advice," Mr Pickles told BBC1's Andrew Marr Show.
"I am really sorry that we took the advice ... we thought we were dealing with experts."
But Lord Smith pointed the finger of blame for the failure to sufficiently dredge rivers at Treasury funding rules.
He said a Treasury-imposed "benefit-to-cost" rule had limited the sum the EA had been able to devote to dredging the silted-up rivers which failed to drain the Levels properly.
It had put the maximum £400,000 on the table it was allowed to, he said, but "the additional funds from other sources that would be needed didn't come in".
"So when politicians start saying it's Environment Agency advice or decisions that are to blame, they need to realise that it's in fact government rules - laid down by successive governments, Labour and Tory - that are at the heart of the problem."
As politicians traded blows on the political fall-out from the disaster, police were investigating whether seven-year-old Zane Gbangbola, who died after falling ill in his flood-hit home in Chertsey, Surrey, may have become a victim of the floods.
Officers have refused to be drawn on whether carbon monoxide poisoning from a generator pumping out flood water from his home may have been to blame, which also saw his parents, Kye Gbangbola and Nicole Lawler, taken ill.
There are more than 230 low-level flood alerts and more than 150 medium-risk warnings in place across Wales and central and southern England with severe weather expected throughout the week.
The Met Office warned that river levels are expected to continue rising along the Thames, the Severn and the Dorset Stour this week.
A further 20,000 sandbags are ready to be deployed to communities at risk of flooding on the Somerset Levels.
Somerset County Council staff have worked tirelessly alongside Royal Marines from 40 Commando throughout the weekend to prepare a further 20,000 sandbags for use.
A Ministry of Defence spokesman said: "Military personnel, currently mostly Royal Marines, continue to provide support in Somerset in areas affected by floods as part of cross-Government and multi-agency relief efforts.
"As the Prime Minister has said, all available resources are being brought to bear to help those still struggling as a result of the floods."
The Ministry of Defence has put 1,600 personnel on six hours' notice to help in the south.
Surrey Police and Thames Valley Police have issued safety advice to residents in their area expected to be affected by flooding.
A spokesman for Surrey Police said up to 2,500 homes are at risk of flooding and added that military assistance is being provided.
The Prime Minister, speaking after chairing a meeting of the Government's Cobra emergency committee yesterday, said he had "made clear again that every resource is available to the local communities affected".
Network Rail had been told to do "whatever it takes" to restore badly disrupted rail links - which earlier saw the south west cut off entirely.
Flooding in Datchet, a village next to the River Thames near Windsor in Berkshire, has forced National Rail to cancel trains this morning.
A statement said: "The River Thames has flooded at Datchet and other locations between Staines and Windsor & Eton Riverside.
"Because of this, trains are unable to run and a replacement bus service is not available."
Flooding has also disrupted services between Oxford and Radley and services are unable to run between Bridgwater and Taunton.
Services from London to the South West remain disrupted after days of severe weather and the rough seas that caused damage to parts of the track and a sea wall at Dawlish.