The cost of damage from flooding and coastal erosion in Britain could rise by 20 times over the next century, according to a government study.
Floods in October 2000 devastated Lewes in East Sussex
The Foresight Flood and Coastal Defence Project involved 60 experts in climate change, engineering and economics.
The study, published on Thursday, said the figure could be cut drastically if emissions of greenhouse gases were reduced.
It also recommends higher spending on flood defences and better planning.
The government's chief scientist, Sir David King, introduced the report looking at the potential costs of flooding and coastal erosion in Britain over the next 30 to 100 years as "the most wide-ranging analysis of future flood risk ever made in the UK".
"There are currently around £200bn worth of assets and 1.7 million properties in flood risk areas in England and Wales," he said.
"The challenge of increased flood risk needs to be considered now."
The report looks at the effects of climate change on coastal and riverside communities in the future, including the human cost to residents.
BBC environment correspondent Tim Hirsch said the study concluded that in the most extreme scenario, and with existing defences, the damage could rise from about £1bn a year now to £20bn by 2080.
He said the experts argued the bill could be reduced greatly by action to curb global warming.
However, even with the most optimistic scenario for cutting greenhouse gas emissions, the cost would still double, our correspondent reported.
People living in flood-hit areas are also expected to suffer a cost to their physical and mental health, the project believes.
The communities likely to be worst affected are in Yorkshire, Lancashire, Lincolnshire and the South East.
The study argues for a steady increase in spending on flood defences and better planning to avoid more homes being put at risk.
The government has said it will use the findings to help draw up a new strategy on flooding and coastal defence, due this autumn.
Environment Minister Elliot Morley said: "Government spending on flood and coastal defence has risen significantly in the last three years, and the UK is firmly committed to combating climate change.
"But this very useful 'What if?' report underlines the need for the government's flood management programme to keep evolving to face up to new potential risks and challenges."
The last serious floods in 2000, caused by rivers overflowing after weeks of heavy rain, resulted in 10,000 homes being inundated.
Mary Dhonau, of the National Flood Forum, told BBC News 3ft (91cm) of "stenching sewage" had filled her Worcester home when the River Severn flooded in 2000.
She is calling on the government to "act now". "They have got to find more money," Ms Dhonau told BBC News.
"A lot more money has to be sunk into flood defence."
Government grants could also help homeowners become more "flood resistant", Ms Dhonau added.