A think tank has warned that there are around 70,000 homes that are at risk of having no flood insurance because they are built in high-risk flooding zones.

High and dry: Preventing tomorrow’s ‘flood ghettos’, published by the conservative think tank Bright Blue, defines properties ‘at-risk’ of at some point becoming uninsurable as those built after 2008 and located in postcodes in what Government and public authorities deem Flood Zone 3, defended or undefended.

A majority of these 70,000 at-risk properties are in Greater London. Other notable potential flooding insurance blackspots include Hull and Somerset.

Around 20,000 of the 70,000 at-risk properties are in areas without flooding defences. Lincolnshire, containing Boston, South Holland and East Lindsey local authority districts, stands out as the county with the greatest concentrations of undefended at-risk properties.

About £31bn worth of properties have been built after 2008 in Flood Zone 3, although a substantial proportion of this is protected by the Thames Barrier. About £5bn is undefended.

There are 3,000 properties out of 70,000 that are ‘greatly at risk’, since they are not covered by Flood Re insurance and are located in areas where at least half of all residential properties have a 1-in-30 or higher annual chance of flooding, irrespective of defences.

The areas of England with the highest concentrations of greater at-risk properties include near the confluence of the Rivers Quaggy and Ravensbourne in Lewisham; the outskirts of Mexborough near Doncaster; and an area near where the Stour branches in central Canterbury.

‘Government policy over the past decade has seen individuals as entirely responsible for finding out their flood risk, but obviously many are simply not aware,’ said Helen Jackson, associate fellow of Bright Blue and author of the analysis.

‘Many of those seeing their communities deal with flooding would view this onus on them as individuals to have understood how flooding could affect them as a bit heartless. Government needs to step in to make sure people are informed.

‘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. 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 focus 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.’