Tory defectors 'could boost Labour'

Tory voters deserting the party for the UK Independence Party could put Ed Miliband in Downing Street, according to polling by former Conservative Party deputy chairman Lord Ashcroft.

Polling over the summer found Labour's lead in its top Tory-held target seats has widened over the past two years, largely because Conservative voters are defecting to Ukip.

Almost 13,000 voters in the Conservatives' 40 most marginal seats were questioned for the survey. In the 32 where Labour was second at the last general election, its lead over the Tories since 2011 has grown from 9 to 14 points, despite a one point fall in its support to 43%.

Over the same period however, the Conservatives fell to 29% - a six point drop - while Ukip enjoyed a six point surge to 11%, with the Liberal Democrats trailing in fourth place on 8%, a fall of one point.

Lord Ashcroft said the figures represented a 8.5% swing from the Conservatives to Labour in these seats - enough for Labour to win all 32 of them, plus a further 66 if it were repeated in Conservative-Labour contests elsewhere.

"The tripling of UKIP's vote share in marginal seats since 2010 threatens to put Ed Miliband in Downing Street in spite of Labour's lukewarm appeal," he said.

"For the Conservatives, the challenge of remaining in government, let alone winning an overall majority, is formidable. But I think the contest will be close and enthralling."

:: Lord Ashcroft Polls questioned 12,809 voters in the 40 most marginal Conservative-held seats between August 1 and September 5.