Around 2,000 homes and businesses in West Lancashire at risk of being lost by 2050

The research examines how rising sea levels caused by climate change, combined with erosion of foreshores by waves, are increasing coastal flood risk, and warns it may not be possible to protect some communities.

The national assessment warns that 20 local authorities have 2,000 or more properties at risk – West Lancashire, North Somerset, Sedgemoor, Eastbourne, Wyre, North East Lincolnshire, Warrington Swale, Dover, Portsmouth, Tendring, Ipswich, Gloucester, Bristol City, Maldon, Adur, Cornwall, East Devon, East Lindsey, and East Suffolk.

However, it has not looked 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.

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.

The study, which is published in the journal Oceans And Coastal Management, compares the rising risk of coastal flooding with existing policies for managing the coast.

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 realign 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 per cent 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.

Those most at risk are single communities, those with dispersed clusters of homes and buildings on a long flood plain such as the Somerset Levels, areas with a narrow space between the shoreline and rising ground, and small quay and coastal harbour communities of the type found across Cornwall.

Lead author Paul Sayers, an engineering consultant who works with the University of East Anglia’s Tyndall Centre and has conducted analysis for the Climate Change Committee, 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.”

Responding to the study, 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.”