A poll by former Conservative party deputy chairman Lord Ashcroft has found Labour could win "a comfortable majority" in the 2015 general election.
Lord Ashcroft polled more than 26,000 voters in 26 marginal constituencies that will be hotly contested battlegrounds between Labour and the Tories.
He said: "Across the battleground I found a 6.5% swing from the Conservatives to Labour – enough to topple 83 Tory MPs and give Ed Miliband a comfortable majority. But this is a snapshot, not a prediction."
He added: "The research also found that most voters in these seats are optimistic about the economy, and only three in ten would rather see Mr Miliband as Prime Minister than David Cameron. Half of voters say they may change their mind before the election – and there is still a year to go."
UKIP's successes in the local elections have raised the possibility of them winning a Westminster seat at the general election.
A year ahead of the general election, Ed Miliband's party is seeing only patchy support in areas it should expect to gain ground.
UKIP are likely to make Rotherham a key target for 2015 after a storming result in the local elections.