The latest YouGov poll puts Jeremy Corbyn’s Labour just three points behind Theresa May’s Conservatives as the election race tightens.
The pollster also has projected that the Tories could lose seats, leaving Britain will a hung parliament after the general election on June 8.
But the Economist Intelligence Unit (EIU) is still forecasting that the Conservatives will be returned to power with an increased parliamentary majority.
Danielle Haralambous, UK Analyst at the EIU, said the Tories are on track to win a majority but not the landslide victory that Mrs May had hoped for.
General election polls: Will Jeremy Corbyn or Theresa May win the election?
“It was a political gamble to call an election in the first place and it is not turning out quite how she expected,” Ms Haralambous said.
“There is a risk of a majority that is slim enough to dent Theresa May’s authority.”
Ms Haralambous said that the Conservative campaign has been “disastrous” and Mrs May's U-turn on social care had been a particular low point.
But she said that the a majority of the public still trust the Prime Minister more on Brexit, adding: “We think Corbyn is unelectable.”
She added that the Conservatives are likely to get between 360 and 390 seats, while Labour could get between 200 and 230 seats.
General election polls: This is the latest poll from Ipsos Mori
The Labour leader has performed better than expected but the latest polls show that the public still believe that Mrs May would be more capable.
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In its most recent forecast, the EIU said: “Labour has picked up support following the release of its left-wing manifesto and an uptick in the approval ratings of its leader, Jeremy Corbyn, whose campaign has otherwise been hampered by blunders.
“Theresa May, the prime minister, continues to be viewed as the more competent leader, but struggled to deflect criticism over her social care policy in the Conservative manifesto and subsequent U-turn on the issue in a television interview on May 29th.
“The U-turn has fed into a perception that Conservative policies are poorly thought through and suggests that the party's political dominance has bred complacency.”
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The latest YouGov poll for the whole of the UK put the Tories on 42 per cent with the Labour party close behind on 39 per cent.
The Tories’ three point lead is its smallest of the campaign so far, while support for Labour is currently at its highest.
YouGov’s controversial projection of the election results predicts that the Tories will lose seats, leading to a hung parliament.
General election polls: This is the latest projection from YouGov
But most other pollsters are still predicting a Conservative majority with the latest Panelbase poll giving the Tories an eight point lead.