But new figures by the leading forecaster reveal tactical voting would cost the Conservatives an extra 35 seats, leaving them with just 124 MPs.
Polling guru Professor John Curtice told The Independent the Tories were already facing a parliamentary wipeout, but that tactical voting could drive Labour to a win that could eclipse even Tony Blair’s 1997 landslide victory.
“With an 18-point lead, it’s all over, we are just talking about adding to the scale of defeat, which, of course, is what happened in ’97,” Prof Curtice said.
The Electoral Calculus poll, seen by The Independent, is the first major look at how tactical voting could shape the next general election.
It reveals Labour would pick up an extra 26 seats with Green and Liberal Democrat backers switching to the party, taking it to a total of 440.
The Liberal Democrats would pick up six additional seats from Labour and the Green Party, taking the party to a total of 32, while the SNP would pick up three seats north of the border from Green voters tactically switching allegiance.
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The survey, conducted with polling council member Find Out Now, will set alarm bells ringing in Downing Street and Conservative Party headquarters just over a year before the election, expected in October 2024.
Electoral Calculus chief Martin Baxter said while 2019 saw tactical voting based on Brexit, “the next election is likely to see straightforward anti-Conservative tactical voting”.
“Many Conservative seats, particularly in the south of England, are at risk,” he told The Independent.
Find Out Now boss Chris Holbrook said the poll showed “tactical voting is being used as a tool to punish the Conservatives”.
Prof Curtice said a willingness to vote tactically was a “relatively rare disposition” as people have to “hate one party and be indifferent between two others”.
“But there are enough of them around in the circumstances at the moment, where you have a deeply unpopular government,” Prof Curtice said.
However, he added, the scale of tactical voting could diminish before the election “if the unpopularity of the government diminishes”.
The poll comes just weeks before a crunch by-election to replace former culture secretary and Boris Johnson loyalist Nadine Dorries – who finally quit her Mid Bedfordshire seat in August.
Polling experts have warned tactical voting will be key for Labour or the Lib Dems to clinch the contest, with a split vote potentially paving the way for Tory candidate Festus Akinbusoye to hold onto the seat.
Tory peer and elections expert Lord Hayward told The Independent: “You have the potential for a split opposition vote because Keir Starmer’s determination to prove he can appeal to all parts of the country has surprised the Lib Dems.”
Mr Sunak will also be forced to defend the Tamworth seat after former Tory whip Chris Pincher resigned as an MP last week after losing his appeal against a suspension for drunkenly groping two men.
And it comes just weeks after Labour and the Lib Dems overturned huge Conservative majorities in the Selby and Ainsty and Somerton and Frome by-elections respectively. Both results were attributed to tactical anti-Conservative voting.
An earlier poll by Electoral Calculus showed the Tories are set to lose all of the 42 seats they hold in the red wall, won by the party at the last two elections but which have historically supported the Labour Party.
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