Voters in “bellwether” coastal seats have swung back behind the Labour Party after supporting Boris Johnson’s Conservatives in 2019, a think tank has claimed.

People living within five miles of the sea said they would vote for Labour over the Tories by a margin of 44% to 24%, with the Liberal Democrats on 11%, according to a poll carried out by think tank Labour Together.

Coastal communities have disproportionately backed winning causes over the last 40 years, with three-quarters supporting Margaret Thatcher in 1987 before Tony Blair doubled Labour’s number of seaside seats in 1997.

Most coastal seats supported Brexit and around 70% voted Conservative in 2019.

That position now appears to have reversed again, with Labour enjoying a net favourability rating of 7% among coastal voters, while the Tories have slumped to minus 32%.

The results of the survey represent a boost for Labour in an area recently described by centre-right think tank Onward as “the forgotten battleground that could decide the next election”.

The think tank warned in September that coastal communities are “in crisis” due to deindustralisation and a decline in tourism, leaving them among the poorest areas in the country.

Josh Williams, director of strategy at Labour Together, said: “Where the coast goes, the country follows.

“Take a look at the polls now and the story is clear: the tide is turning, and the Tories are at risk of being swept away.”

The same survey found that Labour enjoys a four-point lead over the Conservatives in rural constituencies, and an overall lead of 21 points.

– The Labour Together poll surveyed 4,981 British adults between October 27 and November 1.