Labour still has a significant lead over the Tories in key marginal seats despite the virtual dead heat nationwide, according to a poll.

The ComRes/ITV News survey put Ed Miliband's party ahead by 40per cent to 31per cent in 40 swing seats where they are expected to be head-to-head with the Conservatives.

Labour's advantage has increased by a point since November, in contrast to UK-wide polls that have generally shown the gap narrowing.

The Tories do not appear to have benefited from a three point fall in Ukip's vote share in marginals, to 15per cent.

The Liberal Democrats and the Greens were each up one on 8per cent and 5per cent respectively.

Although David Cameron is regarded as more competent and statesmanlike than Mr Miliband, only 12per cent say they will decide how to vote based on who would make the best prime minister.

The Conservatives are most trusted to steward the economy, by 35per cent to 23per cent, while Labour leads on the NHS by 38per cent to 20per cent.

Tom Mludzinski, head of political polling at ComRes, said: "While national polls suggest the race is neck-and-neck, this look at the key battleground seats reveals Labour are enjoying a healthier lead in important areas.

"More than ever before, this election is about winning these important battles and Labour's lead in the marginals will bring comfort where national polling has given them some cause for concern."