The piece in the GE2015 jigsaw that even Lynton Crosby is unable to fix: LAB gets more seats than CON for the same vote shareJanuary 22nd, 2014
What happens when you put CON 35% and LAB 35% into the Electoral Calculus seat calculator http://t.co/qP4NIfGVIM
— Mike Smithson (@MSmithsonPB) January 21, 2014
The challenge for the Tories is even bigger than the projection
Everybody who follows UK politics knows that Labour can secure more seats on a given national vote share than the Tories or other parties.
The above shows what happens on Martin Baxter’s Electoral Calculus seat porjector when vote shares of CON 35/LAB 35/LD 12/UKIP 10 are input.
The calculation on the number of seats is made by applying the changes on a uniform national swing basis on the GE2010 result to each of the GB seats.
Part of the reason things are easier for Labour are the boundaries. LAB seats on average last time were 2,000-3,000 smaller than CON ones but that is only a small part of the picture.
The big driver of the “bias” is that LAB voters are generally more reluctant to turn out where the outcome is not in doubt particularly in Conservative and Labour hearlands.
Where it does matter, in the marginals as we’ve seen election after election, the Labour machine gets its vote out and is particularly skilled at securing anti-CON tactical votes.
Thus, as the Ashcroft and UKIP polling has shown, there is a disproportionate move in the LAB-CON marginals putting many more seats at risk for the blues than would go in a uniform swing.
On my reading LAB could come out with a majority even if on the popular vote it is 2% behind.
What do the Tories do? The aborted boundary plan would have added about 12 seats to the party total which would have helped some way but only so far.
Differential LAB turnout and tactical voting are what does for the Tories and the signs are that these could happen again.