The Conservatives will fail to win a majority in this week's general election, according to a YouGov election model cited by Reuters.
The predictor suggests Theresa May's party will win 305 seats, 21 short of the figure needed to win an overall majority.
If the predictor is accurate, May will have to seek a coalition with another party, or risk Labour leader Jeremy Corbyn forming his own alliance to secure a workable majority.
May, who called the snap election claiming she wanted a decisive mandate ahead of the Brexit negotiations, has been heavily criticised for her performance so far in the campaign, notably her refusal to debate Corbyn and the other party leaders.
Corbyn, meanwhile, has been praised for his performance, and the gap between the two major parties has steadily closed according to the opinion polls.