I've just returned from ConservativeHome's Victory 2015 conference, where Lord Ashcroft (recently profiled for the NS by Andrew Gimson) presented the findings of his huge new marginals poll. These are the seats that elections are won and lost in, so Ashcroft's survey of 19,000 voters in 213 constituencies is the best guide we have to who would win were a general election held today. Polls like this answer the questions that national surveys cannot. Is Labour just piling up votes in its northern and Scottish strongholds? How many seats can the Tories hope to win off the Lib Dems? How many seats can Labour hope to win off the Tories?
Ashcroft's poll shows that although the swing to Labour is lower in the marginals than nationwide (largely due to first term Tory MPs benefiting from an incumbency effect), Ed Miliband would still enter Downing Street with a majority of 84 after a net gain of 109 seats (leaving Labour with 367 MPs). This compares to a majority of 114 on a uniform national swing.
While the Conservatives would win 17 seats off the Lib Dems (including Eastleigh), these gains pale in comparison to the losses they would suffer. Ninety three of the Tories' 109 most marginal seats would fall to Labour, with the biggest swings in the Thames estuary (10.5 per cent) and the Midlands (9.5 per cent). As I've written before, the defection of left-leaning Lib Dem voters to Labour in these seats means the Conservatives will struggle to remain the largest single party, let alone win a majority. There are, for instance, 37 Con-Lab marginals where the third place Lib Dem vote is more than twice the margin of victory.
In addition to gaining 93 seats off the Tories, Labour would win 13 off the Lib Dems, with a 17 per cent swing to the party in those seats where it is in second place. All but two of the latter would fall to Labour as well as two seats – Cambridge and Leeds North West – where it is currently third.
The poll will gladden Labour hearts and darken Tory ones but it's important to remember, as Ashcroft says, that it is "a snapshot not a prediction". It tells us what would happen were a general election held today, not what is likely to happen in 2015. Governments invariably gain support in the run-up to a general election as the opposition comes under greater scrutiny (2010 was typical of this), so Labour needs a large cushion of support to be confident of victory. A similar poll conducted by PoliticsHome in September 2008 suggested the Conservatives would win a landslide majority of 146 seats, while another, carried out in October 2009, pointed to a Tory majority of 70. Just seven months later, Cameron was left with no majority at all. In other words, two years out from the general election, only the most optimistic Labourite or the most pessimistic Tory would treat this poll as a reliable indicator of the result.