The Chartered Institute of Loss Adjusters (CILA) calculates domestic claims will reach £825m, while those from businesses will add up to £680m.
Prime Minister Gordon Brown, who is due to visit affected areas this weekend, has pledged to do everything in his power to help victims of the flooding.
Appeals have been set up in the north of England to assist them.
CILA says there have been 27,500 domestic claims with an average value of £30,000, and 6,800 claims from businesses averaging £100,000.
It added that virtually all properties where there is a claim have now been visited by its members, and the rest should have had a visit by the beginning of next week.
Downing Street has rejected suggestions that the Government has been slow to react to the floods crisis.
Mr Brown promised to make emergency aid available to the thousands left homeless.
He told the BBC's Breakfast: "There will be a comprehensive programme, not just to deal with the immediate problems but also with the recovery."
Mr Brown added: "We know that more has got to be done - with the clean-up, then to help people in distress, then to get the schools back, then of course to repairs.
"We're putting more money in to help the distressed areas."
Mr Brown also pledged to provide assistance to newly-launched appeals.
The South Yorkshire Flood Disaster Relief Fund will raise money for those affected in Doncaster, Barnsley, Rotherham and Sheffield.
And the city council in Hull, where more than 16,000 homes were affected, has launched the Hull Flood Fund.
Archbishop of York Dr John Sentamu has visited Hull, which has seen 10,500 homes evacuated.
Dr Sentamu met people who have been left homeless, as well as council officials, clergy, church members and volunteers.
The Archbishop said: "The poorest, the most vulnerable people on very low incomes - when these things hit them, it hits them hard, and you just feel your soul is almost, as it were, wrenched out."
Communities Secretary Hazel Blears, who visited Sheffield on Thursday, is also due to visit Hull.
Parts of north Doncaster remain underwater on Friday, with mayor Martin Winter expected to outline the town's next move in its battle to return to normality.
Insurance warning
Mr Winter said of the South Yorkshire appeal fund: "We hope that funding collected through the appeal will contribute towards relieving some of the distress caused by the flooding across South Yorkshire."
He warned that it may take between six and 18 months before some residents can return to their homes, "if at all".
As well as money, local residents are being asked to donate unwanted furniture to those affected.
Hull City Council leader Carl Minns, who earlier dubbed Hull the "forgotten city" of the flooding, said: "There's a massive humanitarian disaster here that we've set up an appeal fund for - the Hull Flood Fund - and I appeal to people across the country to donate, so we can help those 35,000 [affected] people get back to normal as well."
He says it could cost more than £200m to repair the damage done to schools, public housing, doctor's surgeries, roads and leisure centres in the city.