Separate polls have handed both Labour and the Tories two point leads as the tight race for Number 10 shows no sign of opening up.
The Conservatives were ahead in the latest ICM poll for the Guardian but at 34% were down five points on their position a week ago. Then pollsters found David Cameron's party at a remarkable 39% and holding a six point lead.
ICM's latest poll has Labour down one point on 32%, with Ukip up four on 11% and the Liberal Democrats up 2 on 10%.
Martin Boon of ICM Unlimited said the Tory lead only emerges when results are weighted based on voters most likely to turn out.
He told the Guardian: "When the race is this tight, the methodological judgments made by us pollsters can become all-important."
The leading parties were reversed in a new Populus poll. Labour were unchanged on 34%, while the Conservative Party was down one, on 32%.
Populus recorded Ukip up one point on 15%, and the Liberal Democrats up one on 9%.
ICM interviewed 1,003 adults by telephone between April 17 and 19 while Populous interviewed 2,048 adults online on the same dates.
Meanwhile, another poll has found university students are around five times more likely to vote Labour or Tory than they are Liberal Democrat.
It reveals that the two major parties are tied for support on the UK's leading university campuses at 31%.
But just 6% of the more than 13,000 final-year undergraduates questioned said they plan to back the Lib Dems on May 7 - a figure the authors of the survey suggested is linked to the party's U-turn on tuition fees.
Students in the final year of a degree were the first to pay the higher, £9,000 maximum tuition fee introduced under the coalition Government in 2010 - months after the Lib Dems campaigned on a pledge to oppose any hike.
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More than half (53%) of those polled said they would not vote for the Lib Dems because of the tuition fee increase.
The latest poll, published by High Fliers Research, shows that 25% of students plan to vote for the Green Party, while 3% are backing the SNP and 1% are in favour of Ukip.
It puts the Conservatives in front at 14 out of the 30 universities in the survey, with support the greatest at Loughborough, while Labour are the front-runners at 11, with support the greatest at Liverpool University.
The Green Party is top at Leeds, while the SNP is leading at Strathclyde and Glasgow and Sinn Fein is the top choice at Queen's University Belfast.
Around 14% of students said they were undecided about which party to support or did not intend to vote.
More than nine in 10 (91%) said they plan to back the party they think has the best policies, while just over half (52%) said the next government's main priority should be to reduce the deficit.
Around two fifths (41%) intend to vote for the party with the most convincing leader, 44% think it will make little difference to them who wins next month, and nearly a third (32%) say they will be voting for the party their parents support.Suggest a correction