Thousands of homes along the River Thames are threatened with flooding as water levels continue to rise.
Fourteen severe flood warnings are in place in Berkshire and Surrey, while two remain in Somerset.
Amid criticism of Environment Agency head Lord Smith, PM David Cameron - who is in flood-hit Dorset - said it was not the time to change personnel.
A minister will answer an urgent question put by Labour in the Commons on the flooding crisis later.
Speaking from Portland, off the Dorset coast, Cameron said: "I am only interested in one thing and that is making sure that everything government can do is being done and will go on being done to help people through this difficult time.
"There will be time later on to talk about things. Right now everybody's got to focus on the job in hand."
Speaking earlier, Lord Smith said his staff knew "100 times" more about flooding than any politician and pointed out that they were bound by rules laid down by government.
He has insisted again he will not resign.
Communities Secretary Eric Pickles previously said ministers had been given bad advice by the Environment Agency over river dredging.
Meanwhile, Environment Secretary Owen Paterson and Pickles are thought to be at odds over the performance of the Environment Agency.
No 10 did not deny Paterson had complained about his colleague, who is standing in for him after he had an eye operation, but said both were doing an "excellent job".
Earlier, Deputy Prime Minister Nick Clegg, who was in Burrowbridge in Somerset today, said dredging should have been done over the last few years but added: "I don't think now is the time to point the finger of blame."