Tens of thousands of new homes built in flood-prone areas of England are at risk of being denied insurance for flood damage in future, according to a new analysis from think tank Bright Blue, flood-related costs are set to soar as the climate threat increases unless changes are made to planning rules.

A study of land registry data released today by the liberal-conservative think tank found there may be up to 70,000 residential properties built since 2009 in areas of England deemed by authorities to be flood zones, and which face being left with no insurance as flood risk increases in the coming decades.

These homes are particularly at risk of being left without insurance for flood damage in future, as they are ineligible for the government and industry Flood Re insurance scheme, which only covers homes built before 2009, the study explains.

Moreover, around 20,000 of these properties lie in postcodes without any flood protection defences at all, including parts of Boston, South Holland, and East Lindsey in Lincolnshire, which has the greatest concentrations of undefended, flood-threatened properties, according to Bright Blue.

It found some £31bn-worth of properties have been built after 2008 in flood prone areas of England - including areas in Lincolnshire, Somerset, and Yorkshire - while around £5bn of these homes remain without any defences against floods.

The report comes amid devastating storms which have left many homes, businesses, and infrastructure damaged by floods in recent weeks, leading to widespread calls for greater investment in flood and climate resilience measures to protect homes. Environment Agency chair Emma Howard Boyd this week spelled out her priority to "build climate resilience into everything we do", signalling a change in tack to focus on enhancing flood resilience as well as building defences.

But Bright Blue said a host of wider planning and building regulation reforms were needed to better protect householders from flooding and insurance risk. It suggested the government consider a later cut-off date for its Flood Re scheme, and called for new mandatory Flood Performance Certificates for all new homes to provide prospective buyers with clear information on flood resilience.

It also said house sellers, conveyancing solicitors or landlords should have to provide flood risk reports to people purchasing properties, and called for building regulations and the National Planning Policy Framework to be strengthened to boost flood protection measures.

Study author Helen Jackson, Bright Blue associate fellow, said many residents in England were likely "simply not aware" about their responsibility for insurance, nor that their homes lie in highly flood-risk areas. As such, many residents may view current policy as "a bit heartless", she added.

"It would be the height of naivety to believe that homebuyers understand their flood risk in a changing climate - including potential uninsurability - when accessible public information isn't yet available on future flood risk," said Jackson. "As a society we mustn't sleepwalk into loading the costs of climate change onto those least able to bear them."

"There needs to be a renewed focussed on dealing with flood risk as a dynamic, not a static, issue, and a much stronger presumption in policymaking that the transition to a flood resilient society won't just happen without government intervention," she added. "Government needs to step in to make sure people are informed."

Bright Blue calculated there may be 3,000 homes of the 70,000 which are "greatly at risk" because they are not covered by the government's flood insurance scheme, in addition to being located in areas where at least half of the properties have a one-in-30 or higher chance of flooding.

Areas of England found to have the highest concentrations of these greater flood-risk properties include those near the confluence of the Quaggy and Ravensbourne rivers in Lewisham, South East London, homes on the outskirts of Mexborough near Doncaster, and areas close to the Sour River in Canterbury, according to the study.

The Department for Environment, Food and Rural Affairs (Defra), which is currently in carrying out a review of flood insurance policy, said planning and location of new homes was the responsibility of local councils.

"However, flooding risk should always be a consideration to ensure building takes place where this risk is lowest," it said in a statement. "Where development in a risk area is absolutely necessary, sufficient measures should be taken to make sure homes are safe, resilient and protected from flooding."