(Bloomberg) -- Prime Minister Boris Johnson’s Conservative Party is on track to win a smaller majority than previously projected in the U.K.’s general election, according to a hotly anticipated poll published two days before voting.

The Tories will win 339 seats in the House of Commons, Labour 231, the Scottish National Party 41, and the Liberal Democrats 15, according to a YouGov poll on Tuesday, which used a technique that more closely predicted the 2017 election than standard surveys. When smaller parties are included, that would give the Conservatives a majority of 28 seats. That’s smaller than in the previous iteration of the poll two weeks ago, which projected a majority of 68.

Earlier on Tuesday, Johnson warned activists against complacency. “This is a very, very close-fought election, and we need every vote,” Johnson said at a campaign event in Uttoxeter, central England, saying his party is “absolutely not” home and dry.

Through a process called Multilevel Regression and Post-stratification, or MRP for short, YouGov aims to identify different types of voters, and predict their behavior. Then the company works out how many of each of these voter types there are in each electoral district to produce a forecast.

In the 2017 election, YouGov’s MRP poll correctly predicted that Theresa May would lose her majority, at a time other polls were suggesting her Conservatives would secure a big win.

To contact the reporter on this story: Thomas Penny in London at tpenny@bloomberg.net

To contact the editors responsible for this story: Tim Ross at tross54@bloomberg.net, Robert Jameson, Robert Hutton

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