By Ian Dunt
The Liberal Democrats have overtaken Labour in the first set of polls to come through since last Thursday's TV debate.
A YouGov poll for the Sun put the Conservatives on 33%, the Liberal Democrats up eight points to 30% and Labour lagging behind on 28%.
This evening two polls underlined rapid Lib Dem progress. According to a ComRes poll for the Sunday Mirror and the Independent on Sunday, Nick Clegg's party were in second on 29% behind the Tories on 31%. Labour slipped to third, on 27%.
A poll for the Sunday Telegraph by ICM saw the Lib Dems in third place, on 27% to Labour's 29% and 34% - but most of the research for this poll was done before Mr Clegg's successful appearance on Thursday evening's leaders' debate.
"I think something exciting is happening," Mr Clegg told Sky News.
"I think more and more people, a growing number of people, are just starting to believe that we can do something different this time.
"I think a growing number of people are starting to hope that real change and that real fairness is finally possible in Britain."
Speaking later in Hull, however, the Liberal Democrat leader tried to calm down the media response, saying: "I think people are getting a bit hyped up about this. It's just one leaders' debate."
The shocking poll result is just the latest indication of how well Nick Clegg's performance came across to voters on the debate, which was watched on ITV by nine million people. Several instant polls branded him the winner at the time, but today's YouGov survey was the first of the traditional daily polls to substantiate Thursday night's data.
Of the eight points the third party won, four came from the Conservatives, three from Labour and one from smaller parties.
The way in which the votes have been salvaged from the other two parties appears to vindicate Mr Clegg's arguments to the Lib Dem conference last year that the party could fight the Conservatives in the south and Labour in the north.
But there as also a significant boost in support from the young, with 44% of 18 to 34-year-olds supporting Mr Clegg.
It is the first time the Lib Dems have overtaken either of the two larger parties since 1983, despite dire warnings at the height of new Labour that the Conservatives would soon become the third party.
But the success brings fresh attention to the Lib Dems' policy, and party officials are now warning that it will be under far greater scrutiny than ever before.
Labour and the Tories adopted altogether different retaliation strategies to the resurgent Lib Dem threat today.
Alan Johnson urged greater cooperation between the two progressive parties and suggested a Labour/Lib Dem coalition in the event of a hung parliament would not be a problem.
Meanwhile, David Cameron and Ken Clarke urged voters to give the Tories an emphatic victory so as to prevent a hung parliament, which they branded undemocratic and economically dangerous.