David Cameron's pledge to hold a referendum on EU membership if the Conservatives win the next General Election appears to have given the party a boost in the polls.
A survey conducted in the wake of the Prime Minister's speech on Wednesday showed the Tories had enjoyed a five-point jump from last month, mostly at the expense of the eurosceptics of UKIP.
The poll, by ComRes for the Sunday Mirror and the Independent on Sunday, put the Tories on 33%, with Labour stood still at 39% and the Liberal Democrats up two at 11%.
UKIP, which has registered significant advances in recent months, fell back four points to 10%.
Mr Cameron has insisted he wants to stay in the EU but said he would aim to renegotiate the relationship before offering voters the choice whether the UK should stay in under the new terms or leave.
However, despite the resurgence in the latest polls, many voters backed Labour and Lib Dem warnings that Mr Cameron's position would cause "years of uncertainty which will be bad for the British economy" by 43% to 30%.
The majority also now believe that leaving the EU would in itself be bad for the economy in terms of lost jobs and trade - by 38% to 36%, a turnaround from November when 40% disagreed and 36% agreed.
There was also a significant shift in the numbers saying the UK should quit Brussels regardless of whether powers could be returned, voters disagreeing by 43% to 33% - the exact opposite of the previous poll.
Other polls also showed a post-speech Tory bounce.
One by Survation for the Mail on Sunday put the Tories up two at 31%, Labour stable at 38%, UKIP down two to 14% and the Lib Dems down one at 10%.
Exactly half of those polled said they favoured a UK exit, but of those more (43%) said they would consider switching to the "yes" camp if significant powers were returned than wouldn't (36%).
An Angus Reid Public Opinion for the Sunday Express showed a three-point rise for the Conservatives to 30% with Labour dipping three to 39%.
The success of Mr Cameron's EU speech , however, has not stopped speculation within the party about his possible successor should he fail to secure a majority at the next election.
Several Sunday newspapers reported that MPs had been approached about whether they would consider supporting Adam Afriyie, an IT millionaire who became the Tories' first black MP in 2005.
The latest polls were released as Labour leader Ed Miliband - who has said the party is not in favour of the referendum promised by the Prime Minister - faced renewed calls from within his own party for an immediate in/out referendum.
Former Europe minister Keith Vaz, a supporter of EU membership, said it was "time to settle the question of Britain's membership in the EU once and for all".
"I support a referendum because, like David Cameron, Ed Miliband and Nick Clegg, I believe the future of our country is in Europe. I am supportive, but pragmatic about the European project," he wrote in the Sunday Mirror.
"I accept British people rightly feel the EU is not delivering on its promises. Reform is necessary. We need better, stronger and earlier scrutiny by Parliament of EU measures."
UKIP leader Nigel Farage told the Sunday Express his party would now be "going for the Labour Party's jugular" over its failure to back the referendum.
"Here was an open goal for the Labour Party to demand that referendum now. They could have called his bluff. Ed Miliband could have pressed the Prime Minister to give voters a say on Europe without ifs and buts. Yet they didn't," he wrote.