Investment in flood defences must increase significantly or four times as many properties in England could be at serious risk of damage over the next 20 years, the government’s climate change advisors will warn today.

As swathes of the country continue to battle with flood waters, the report by the Committee on Climate Change’s Adaptation sub-Committee (ASC) will argue that despite some improvements around 20 per cent of development on flood plains is still being built without community defences.

It warns that as a result around 40,000 homes and businesses at high risk of flooding, although the ASC was unable to ascertain how many of these properties have dedicated property defences or are part of estates with in-built resilience features.

In total, around 210,000 homes and business premises were built on floodplains in the past 10 years, leaving one in seven properties in England facing some form of flood risk.

However, the problem pales in comparison to the situation the country faces over the coming years as climate change is projected to cause even more frequent, and potentially severe, flooding events, while at the same time spending on flood defences is falling.

Funding allocated to flood defences in the current spending review period - 2011/12 to 2014/15 - has dropped by a fifth in real terms compared with the past four years, from £300m a year to £260m.

The ASC calculates the Environment Agency’s promise to deliver 15 per cent efficiency savings will equate to £54m over the four year period, but warns funding needs to increase by £20m a year on top of inflation to keep pace with climate change impacts.

Around 610,000 properties would be at significant risk of flooding by 2035 if funding does not meet the Environment Agency’s required level, the report warns, compared to 160,000 if the money is found to fill a potential £860m shortfall over five years.

The ASC says this leaves Defra with two options: support a “sustained and increased investment” in flood defences from public or private sources or “identify ways to manage the social and economic consequences of more frequent flooding”.

In the previous spending period, the private sector accounted for £3m of the £13m raised from external sources and much of the £72m garnered in this spending period is thought to be from local authorities.

Lord John Krebs, chair of the ASC, told reporters it was “questionable” that private sector funding would be sustained at the necessary level.

“If you project forward out to 2035, there is a growing gap between what the Environment Agency says it needs to spend and what is in its budget,” he said. “Going forward … there will be a growing gap between what needs to be spent to keep current risk levels constant and what is actually going to be spent.”

As well as facing problems presented by too much water, the ASC report also warns the UK is not doing enough to conserve water and use it efficiently, which, combined with the effect of climate change, could see demand outweigh supply by three billion litres per day during the 2020s.

While average water consumption has fallen from 150 litres to 145 litres per person per day over the past decade, this is still among the highest rates in Northwest Europe, and the ASC wants the government and water companies to work harder to lower demand to below 130 litres.

This would entail wider use of household and business efficiency measures and water metering, which should be targeted at utilities likely to be at risk of future of water shortages, such as Severn Trent and Thames, neither of which have large metering roll-outs planned.

“Much of the emphasis of the water company investment is increasing supply, by building new reservoirs,” Krebs said. “We think there is more that can be done to reduce demand. In order to drive that there has to be more use of water metering. We’re saying to the government is don’t just look at water scarcity now. It’s not something you can sit and wait until 2029… it takes a while to build this up.”

A Defra spokesman said the department had reduced the flood risk to 182,000 homes over the last three years and added the new National Planning Policy Framework encourages local authorities to only consider development where it is safe and it does not increase flood risk elsewhere.

“We are spending more than £2.17bn over four years to protect people from flooding and our successful partnership funding model will draw in around an additional £72m,” he said. “The money for flood defences is being spent more effectively than ever before and we now expect to exceed our target to better protect another 145,000 homes by 2015.”

The report comes the day after groundbreaking research (PDF) detailing how climate change has increased the likelihood of extreme weather events was published by researchers from the Met Office and the National Oceanic and Atmospheric Administration (NOAA).

Analysing six key weather events, they found climate change made extreme heat more likely, while the odds on unusually cold periods lengthen. For example, in 2011 parts of Western Europe were almost 1.5 degrees C warmer than can be attributed to weather patterns alone.

“While we didn’t find evidence that climate change has affected the odds of all the extreme weather events we looked at, we did see that some events were significantly more likely,” said Dr Peter Stott, Head of Climate Monitoring and Attribution at the Met Office and one of the editors of the report.

“Overall we’re seeing that human influence is having a marked impact on some types of extreme weather.”