On the eve of the Labour Party conference this research was interesting:  http://labour-uncut.co.uk/2013/09/21/exclusive-uncut-poll-over-1-in-4-2010-lab-voters-have-been-lost-here%E2%80%99s-what-can-be-done-to-win-them-back/

"Out of Labour’s lost 2010 voters, almost 1 in 5 are now supporting the Conservatives (18%)."