The research by the Oceans And Coastal Management Journal suggests 200,000 homes and businesses in England could be lost by the 2050s.
The research examines how rising sea levels caused by climate change - combined with erosion of foreshores by waves - are increasing coastal flood risk.
It warns it may not be possible to protect some communities, including in the South West.
Those most at risk are single communities, i.e. those with dispersed clusters of homes and buildings on a long flood plain such as the Somerset Levels.
Other areas at risk include those with a narrow space between the shoreline and rising ground, and small quay and coastal harbour communities of the type found across Cornwall.
Experts warned there is an urgent need for a national debate about the flooding threat to coastal communities, and for long-term clarity on “transformational change” in some areas, including rolling back defences and moving properties.
Lead author Paul Sayers said: “Significant sea level rise is now inevitable. For many of our larger cities at the coast protection will continue to be provided but for some coastal communities this may not be possible.
"We need a serious national debate about the scale of the threat to these communities and what represents a fair and sustainable response, including how to help people to relocate.”
The analysis says North Somerset and Cornwall are among the local authorities with the largest challenge in responding to sea level rise through to 2050s and 2080s.
England could face around 35cm (14in) of sea level rise compared to historic levels by 2050 and is nearly certain to see close to 1m (3ft) of sea level rise by the end of the century, the study said.
Rising seas combined with increased wave-driven erosion are raising the risk of coastal flooding, forcing the Government and communities to decide how to respond – mainly whether to hold the line against the sea by building and maintaining defences or realigning the shoreline and move properties.
For a thousand miles of English coast (1,600-1,900km), there will be high pressure to rethink the current policy to hold the line as it may become unfeasible due to rising costs, or technically impossible, the study says.
That accounts for around 30% of the coastline where hold-the-line policies are in place, and could affect around 120,000 to 160,000 properties – excluding caravans – by the 2050s, with a proportion likely to need relocating.
The study says it is not possible to say how many of them will have to be moved, as that will be a matter for Government, policy and funding for flood defences.
The figure is on top of the 30,000 to 35,000 properties already identified in areas which have a policy to realign the coast.
The study focuses on the impacts of flooding and does not include properties directly at risk from coastal erosion such as clifftop homes.
The study did not look at local features, or nationally important infrastructure such as nuclear power plants, that would mean the immediate coastline will be protected in the long term.
Jim Hall, Professor of Climate and Environmental Risks at the University of Oxford, said: “We need to have honest conversations with coastal communities that it will simply not be possible to protect every house and business from sea level rise.“
"These changes are coming sooner than we might think and we need to plan now for how we can adjust, including a nationwide strategic approach to deciding how to manage the coast sustainably in the future.”
A spokesperson for the Department for Environment, Food and Rural Affairs said: “We recognise the threat from climate change and sea level rise, which is why are investing a record £5.2 billion from 2021 in flood and coastal defences to better protect properties along our coasts.
“Our Coastal Transition Accelerator Programme is also exploring innovative approaches to adapt to the effects of coastal erosion, and shoreline Management Plans will outline long term plans to manage the risk of coastal change over the next 100 years.”