More than three million households are at risk of flooding but are not being warned by the Government, the National Audit Office (NAO) has said.
Across England, 3.4 million homes are at risk of surface water flooding, which occurs when extreme rainfall overwhelms the drainage system.
But unlike river, coastal or groundwater flooding, households get no advance warning from the Environment Agency to tell them their home may be at risk.
“Government has good forecasting data for droughts, heatwaves and storms, but less so for surface water flooding,” the NAO said.
It added that “surveys show that public awareness of the risk of surface water flooding is low and that people do not know who to report these incidents to when they happen”.
A report last year from the National Infrastructure Commission (NIC) said the Government should consider funding individual flood barriers or insurance for the homes at highest risk.
It has also called for water companies to invest in more natural drainage systems, as existing capacity cannot cope with the rise in population and increased rainfall.
It said the impact of such flooding “can be profound” and pointed to flash floods in London in July 2021 which left Tube stations, hospitals and hundreds of homes deluged.
Emergency services were called out to homes where residents were waist-deep in water after being taken by surprise by the sudden rise of the surface water.
Sir John Armitt, head of the NIC, said at the time that the paving over front gardens with impermeable concrete was exacerbating flooding in urban areas.
Experts have also raised concerns that thousands of homes are being built on flood plains every year, increasing the risk of surface water flooding.
The warning from the NAO comes in a report which says the Government is underprepared for the impact of extreme weather events including storms and droughts.
Excess heat and extreme rainfall are expected to increase in the future in line with temperature increases as a result of climate change.
“The UK’s experience during the pandemic demonstrated the vital importance of building resilience, and that lesson also applies to extreme weather events,” Gareth Davies, head of the NAO said.
“Government needs to place sufficient emphasis on prevention and preparedness - clearly articulating the level of risk it will tolerate - and making informed decisions about prioritisation to ensure efficient and effective investment for the long-term.”
The Government has taken some action, including establishing the third national adaptation programme, which sets out action being taken to adapt to climate change.
But the NAO said ministers need to step up preparation to limit the impact of extreme weather events.
It said the Government does not track or evaluate its spending on extreme weather, meaning it cannot demonstrate whether value for money is being achieved.
The assessment came as analysis by independent experts on the Climate Change Committee suggested that at least eight global warming risks may each cost more than £1 billion a year by 2050.
“Extreme weather events can have devastating consequences for individuals, communities and businesses. They are becoming more frequent and more severe,” said Meg Hillier MP, chairman of the Commons committee of public accounts.
She said that the Government “must place emphasis on prevention and preparedness and make long-term investments to protect people and businesses”.
Cllr Darren Rodwell, environment spokesman for the Local Government Authority, said: “Councils want to play their full role in preparing people and places for the impacts of climate change on local areas.
“As extreme weather events become more frequent and intense, the public sense of unpreparedness will undoubtedly harden and grow.
“Councils are doing fantastic work to tackle climate change and we want our communities to feel secure in their homes and local areas.
“The public trust us most because we are rooted in communities and understand places. We must be given the tools and funding needed to make that happen.”
A spokesman for the Cabinet Office said: “The best way to protect people, businesses and communities from extreme weather events is by having systems in place that are both robust and flexible. This is core to the UK’s resilience strategy, which has been proven to allow us to effectively coordinate the Government and wider resilience community’s response to a diverse set of risks – having successfully dealt with a series of severe weather events this autumn.
“As the Deputy Prime Minister set out this week, we are making excellent progress on building flexible and agile capabilities, systems and strategies which ensure the UK is prepared for emerging threats.
“This includes constantly improving our systems, for example vastly increasing the number of datasets being fed into the National Situation Centre, and launching a new 24/7 Emergency Alerts system in April, which is able to deliver warnings and information to the public.”