LABOUR is on track to seize enough seats from the Conservatives to become the largest party in Westminster after next year's general ­election, according to polling by Lord Ashcroft.

But the survey of marginal seats suggested that the number of voters switching directly from Tories to Labour is smaller in seats where Ukip is performing strongly.

Ed Miliband's party will be further concerned that any complacency about the impact on Labour of the rise of the eurosceptic Ukip could rob them of victory in the May 2015 poll.

The Tory peer's pollsters questioned more than 1,000 voters in 11 Conservative-held constituencies which are not among the Tories' most vulnerable seats but where Labour took second place in 2010 and will be hopeful of winning next year as part of their drive to get Mr Miliband into No 10.

The survey found an overall five per cent swing from Tory to Labour in these seats - enough to snatch nine of them (Brentford & Isleworth, Brighton Kemptown, Corby, Enfield North, Halesowen & Rowley Regis, Hastings & Rye, Hove, Ipswich and Nuneaton).

Lord Ashcroft went on to say that the results suggested at least 29 seats would fall to Labour if the findings were repeated at the general election.