The huge surge in support for the Liberal Democrats continued with a new poll putting the party on 30% - up 10% in a week.
The latest findings are further evidence of the dramatic increase in the popularity of the Lib Dems among voters, and follow a clutch of polls suggesting the election is now a three-horse race.
A Guardian/ICM poll puts them in second place behind the Conservatives, who are on 33% (down four) and sees Labour third on 28% (down three). It is the first time Labour has been in third place since the ICM series began in 1984, and its rating was its lowest since last October.
The Conservative score was its lowest since July 2007 and the same as the party achieved when going down to defeat under Michael Howard in the 2005 election.
It follows a YouGov poll for The Sun which put the Lib Dems on 33% (up three points since a similar survey published on Saturday), ahead of the Tories on 32% (down one), with Labour trailing on 26% (down two).
The dramatic findings are the the latest in a string of polls suggesting the impact of Liberal Democrat leader Nick Clegg's widely-praised performance in Thursday's historic first prime ministerial debate could be even greater than previously thought.
ICM Research interviewed a random sample of 1,024 adults aged 18 and over by telephone on April 16-18.
Earlier, Labour deputy leader Harriet Harman warned that a vote for any other party would help the Tories get into government. Launching Labour's London General Election campaign in Canary Wharf, Ms Harman also hit out at Tory leader David Cameron's "series of soundbites that don't add up".
Meanwhile, Mr Cameron attempted to launch a fightback against Nick Clegg, insisting only a decisive victory for his party could deliver "real change".
Mr Cameron suggested the Lib Dems' surge in the polls following Thursday's TV debate was the result of desperate voters "grabbing on to anything new" in their search for a solution to the country's problems. But Mr Clegg said voters were starting to believe the election may produce a break from the "tired choices" offered by the two parties which have dominated British politics.
