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General election: Why did political pollsters get it so wrong?

Published polls ahead of the 2015 general election proved to be a bad prediction of the results.

The Conservatives won the election, with a majority of 12 seats, but polls ahead of May 7 had suggested they would not win a majority.

Labour's election pollster has said public polls "showed a much more favourable position for Labour than we were finding in our internal data" both before the campaign and during it.

Chris Cook reports for Newsnight.

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