Ed Miliband
The poll gives the Labour Party leader Ed Miliband a small boost ahead of the 2015 General ElectionReuters

The Labour Party has a narrow lead in key marginal constituencies ahead of the 2015 General Election, according to a poll from Lord Ashcroft.

The survey, which questioned more than 12,000 people in 12 Conservative-Labour "battlegrounds", found that Ed Miliband's party led the Conservatives by 36% to 33% – a swing of 4.5% since the 2010 election.

The seats, which have majorities of between 1,936 and 3,744 people, included Erewash, Kingswood, Loughborough and Worcester.

But Lord Ashcroft said the findings from the individual constituencies mean that three of the constituencies would stay Conservative – Loughborough, Kingswood, and Blackpool North and Cleveleys.

"The six-point Labour lead in Croydon Central is the smallest I have yet found in a seat the Tories are defending from Labour in London," the peer said.

"In the North, where the Conservatives are widely expected to struggle, the picture is in fact mixed. In previous rounds we have seen results ranging from a tie in Pudsey to a 14-point Labour lead in Lancaster and Fleetwood.

"In the current selection, though Labour look well ahead in Bury North they would probably expect to be leading by more than one point in both Chester and Wirral West."

The research also revealed that 17% of 2010 Conservative and 9% of 2010 Labour voters said they would vote Ukip in their own constituency.

In addition, the study found that Ukip supporters were the least likely to expect the economy to do well over the next year either for the country as a whole (48%) or for themselves and their families (51%).

Conservative voters (83% and 84%), in contrast, were much more optimistic.

The findings come after a separate poll from Lord Ashcroft found that 30% (-1) of respondents would vote for David Cameron's party if a general election was held tomorrow.

In comparison, 29% (-2) of people would vote for the Labour Party, 16% (-2) would vote for Ukip and 10% (+3) would vote for the Liberal Democrats.