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Labour's loss of thousands of supporters to UKIP handed David Cameron his election victory, a new study has found.

A report by former shadow cabinet minister Jon Cruddas says UKIP cost Labour at least 13 seats at the general election - enough to have stopped the Tories’ overall majority.

He said Ed Balls's humiliating defeat in West Yorkshire was among those caused by the haemorrhaging of votes to UKIP.

“Labour lost more and more voters to UKIP at a slow but steady pace throughout the Parliament,” Mr Cruddas warned.

The Dagenham MP, formally Ed Miliband's policy chief, quit the shadow cabinet in May to study why Labour suffered such a crushing defeat.

(Image: Reuters)

He has previously said three-quarters of the voters Labour have lost since 1997 are working class, highlighting immigration and the economy as key areas where Labour lost trust.

His latest report includes research by Survation which found the Tories were far more successful than Labour at winning back voters they had lost to UKIP since 2010, particularly in the final months of the election campaign.

Mr Cameron focused relentlessly on wooing UKIP voters with his dire warnings about a Labour/SNP alliance.

By contrast Labour appeared to have little strategy for dealing with Nigel Farage's party .

“The Conservatives losses peaked in 2013,” Mr Cruddas said.

“They then recovered some voters, before rapidly recovering a large proportion of them during their aggressive period of campaigning between January and May 2015.”

(Image: Solarpix)

Mr Cruddas estimated around 20% of UKIP voters in 2015 were previously Labour supporters, and published stats showing that had they all backed Ed Miliband he would have picked up 13 more seats from the Tories.

Those seats were Bolton West, Brighton Kemptown, Bury North, Croydon Central, Derby North, Morley and Outwood, Plymouth Moor View, Plymouth Sutton and Devonport, Telford, Thurrock, Weaver Vale, Gower and Vale of Clwyd.

The MP added: “There might well be a number of other constituencies in which the proportion of UKIP support coming from Labour was higher than 20%, so adding further seats to the list.”