The above is based on data from Professor John Curtice on what vote leads LAB and CON require to put them over the threshold of 326 to win an overall majority at GE2015.

This is, of course, calculated on a uniform national swing (UNS) in each GB seat. At GE2010 the Tories over-performed UNS by a bit.

For the Tories more than LAB, click the tab on the chart, the LD share is critical. At a 10% yellow share the Tories could theoretically get by with a lead of just 5.9%.

There are several factors that can skew the UNS:-

Incumbency – where the MP is standing again. All parties saw a benefit at GE2010 with the LDs enjoying the biggest bonus.

First time incumbency where the sitting MP gets an extra bonus.

Targeting of marginals by all the parties can see disproportionate changes.

Tactical voting either increasing or unwinding.

The big message, as I am sure we all know, is that the threshold for Labour is a few points lower than the Tories.

The number crunchers have yet to find a way of including Ukip.

Mike Smithson

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