Nick Clegg is on track to lose in Sheffield Hallam, according to fresh polling data from Lord Ashcroft.

After revising the results of a survey taken in November last year, Ashcroft found the Deputy Prime Minister trailing Labour candidate Oliver Coppard by three points in his current constituency.

Ashcroft's previous poll had the Lib Dem leader in front by three.

In a blog on his website, the Tory peer and respected pollster blamed the misleading data on a new polling company that he said he won't be using again.

Ashcroft was alerted to possible polling problems after a recent survey found Labour in front by ten points.

The result this May in Clegg's home constituency promises to have profound consequences for the national picture.

By targeting Clegg's seat as part of its 'decapitation strategy', Labour hopes to make it more difficult for the Lib Dems to form a new coalition with the Tories.

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Lord Ashcroft revised two other polls amid the reports of misleading data from Sheffield Hallam, and observed that Ukip leader Nigel Farage is performing better in South Thanet than previously thought.

According to November's poll, he was behind the Conservatives by five points when in fact it was just one.

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And in Doncaster North, the constituency represented by Ed Miliband, Labour enjoys a comfortable 30-point lead over second-placed Ukip.

Of the corrected polling, Lord Ashcroft wrote: "I cannot allow this episode to cast doubt on the reliability of my polling more generally.