The Environment Agency issued 14 severe flood warnings - meaning lives are at risk - for the Thames in the affluent counties of Surrey and Berkshire to the west of London.
Some areas are already under water, including parts of the Great Windsor Park, near Queen Elizabeth II's castle at Windsor, which itself is built on higher ground.
London itself is protected by the Thames Barrier, although a suburb to the south of the capital, Croydon, announced plans to divert rising floodwaters caused by heavy rain away from homes and businesses by pumping them into a pedestrian underpass.
Parts of the southwest of England have been under water for weeks after the wettest January since 1766, with more bad weather expected over the coming days.
Forecasters at the Met Office said the run of winter storms, which have brought heavy rain and strong winds and seen high waves batter the English coastline, has been "exceptional in its duration".
But there has been a growing tide of criticism at the official response, which has erupted into a full-blown political row.
Many people in Somerset, one of the hardest-hit counties in the southwest, blame the devastating floods on the failure of the Environment Agency - a government body - to dredge local rivers.
Communities minister Eric Pickles joined the attack on Sunday, suggesting the government "perhaps relied too much on the Environment Agency's advice" on flood prevention.
"I am really sorry that we took the advice... we thought we were dealing with experts," Pickles, a member of Prime Minister David Cameron's Conservative party, told BBC TV.
Chris Smith, the head of the Environment Agency, hit back on Monday and accused ministers for holding back vital funds.
"When I hear someone criticising the expertise and professionalism of my staff in the Environment Agency who know more about flood risk management - 100 times more about flood risk management - than any politician ever does, I am not going to sit idly by," he said.
Smith, a former minister for the now opposition Labour government, said the Treasury had limited the amount the agency could spend on flood management in Somerset.
The prime minister last week announced £130m in extra funding for emergency repairs and maintenance.
Cameron paid his first visit to Somerset, where the Royal Marines have been deployed to help with sand-bagging, on Friday and on Monday was due to tour storm-affected areas in the southwest counties of Devon and Cornwall.