(Bloomberg) -- The UK’s undecided voters are turning away from Rishi Sunak’s Conservatives, according to polling analysis that if replicated in the July 4 general election would extinguish the prime minister’s already slim chances of clinging on to power.

Undecideds are likely to break relatively evenly between the Tories, Keir Starmer’s opposition Labour Party and the right-wing Reform UK, led by Brexit campaigner Nigel Farage, the modeling by the pollster JL Partners showed on Monday. That’s despite the demographic make-up of undecided voters suggesting more should break toward the Conservatives.

“The average undecided voter ought to be voting Conservative: Their age and previous voting habits would strongly suggest this,” said Callum Hunter, data scientist at JL Partners. “However, our model predicts that nearly half of these undecided voters that voted Conservative in 2019 will defect to either Labour or Reform in this election.”

The analysis is yet another blow to the Conservatives, coming after a series of disastrous setbacks for the party that’s governed the UK for the past 14 years. Tory strategists, led by their campaign chief Isaac Levido, have consistently said over the last year that their main route to staying in office was seeing their vote boosted by undecideds overwhelmingly choosing them in the final weeks before polling day.

Last week, the Tories suffered a triple blow as Farage decided to stand in the election, seat-by-seat projections put the party on track to its worst defeat in more than a century, and Sunak’s failure to stay in Normandy for the full itinerary of D-Day commemorations backfired spectacularly. After 19 days of the campaign so far, Bloomberg’s composite poll — a rolling 14-day average using data from 11 polling companies — puts the Tories 21.8 points behind Labour.  

JL Partners said that some 8% of the electorate — around 3.8 million voters — has yet to decide how to vote. Of those, 30% will likely vote for the Tories, while 29% will vote Labour and 28% will back Reform. The figures also account for voters’ likelihood to turn out. Nearly half of people who previously voted Conservative but now say they are undecided are likely to defect to either Reform or Labour, according to the modeling. 

Tory aides have previously claimed that undecided voters did not feel strongly in favor of Starmer or Labour, and therefore their votes could head to Sunak in droves, in what would be a game-changer that hasn’t been picked up by typical voting intention polls.

Yet the final result could be even worse for the Tories as the current numbers do not yet reflect a recent surge in support for Farage’s Reform since he announced his return as the party’s leader last week, nor Sunak’s own goal over the D-Day commemorations on Thursday.

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