The first target for the blues – to be doing better than last time
At GE2010 the Conservatives had a GB national vote share of 37% which was 7.3% bigger than Labour’s total of 29.7%.
So under a uniform national swing CON needs to be ahead by that margin simply to stop losing seats to LAB. That is the starting point for the party at GE15 – to do at least as well as they did last time.
Thus it cannot be assumed that CON lead of 6% is sufficient for them to hang onto all they hold at the moment from LAB.
This all assumes a uniform swing and, of course, the whole political environment is very different with the rise of UKIP. But in terms of the impact on seats it is the gap between LAB and CON that historically has been the best measure. This at GE10 CON moved from being 3% behind LAB to 7.3% ahead.
Note that all the main national polls shares are on a GB basis rather than an all-UK one. For this purpose the Northern Ireland seats are left to one side. Thus it is the GB shares from 2010 that we work from. CON 37, LAB 29.7, LD 23.6.
Of course the Tories have hopes of taking LD seats but here there’s a huge challenge. As is widely known the yellows have a record of outperforming national swing in the seats that they hold, particularly where the existing MP is standing for re-election.
This is being shown again for GE15 in the Lord Ashcroft CON-LD marginals polling. Although on national numbers there’s a huge gap between blue and yellow Lord A’s latest constituency based findings have a LD to CON swing of just 2%. This would curtail many of the expected gains from current margins in national polls.