The Conservatives' advantage over Labour has narrowed to just five points in the first opinion poll taken since Monday night's suicide bomb attack in Manchester.
The YouGov survey for The Times, conducted on Wednesday and Thursday, put the Conservatives down a point on the previous week on 43% and Labour up three on 38 per cent, with
Liberal Democrats up one on 10 per cent and Ukip up one on 4 per cent.
Meanwhile, a TNS/Kantar poll taken before Monday night's atrocity put the Conservatives down five points on 42 per cent, with Labour up five on 34 per cent, Lib Dems up a point on 9
per cent and Ukip down two on 4 per cent.
The results reflect a significant tightening in the race for the June 8 General Election, which was called in April at a point when Theresa May's party was enjoying a seemingly
unassailable lead of as much as 24 per cent over Jeremy Corbyn's Labour.
Labour's former deputy prime minister Lord Prescott, who has given his personal endorsement to Mr Corbyn's drive for Downing Street, welcomed the findings on Twitter: "It's happening!
The YouGov poll showed a steep slump in popularity for both Mrs May and the Conservatives over the course of the campaign so far, and a sharp improvement for both Mr Corbyn and
YouGov questioned 2,052 voters on May 24 and 25. TNS/Kantar interviewed 1,200 adults between May 18 and 22.
The Conservative candidate for Braintree, James Cleverly, tweeted: "Labour has thousands of Momentum activists and millions from the unions. We never thought this election was going
to be a walk in the park."