Tension in the coalition has led many commentators to ask whether it can hold on until the next election. Analysis tends to focus on policy rows and political rifts between the coalition partners, but not on the raw electoral dynamics which are likely to be play a greater role in determining the fate of the coalition. Put simply, the Tories need to wipe out a large number of Lib Dem MPs if they are to stand a chance of governing on their own after 2015, which is bound to put real pressure on the coalition the closer we get to the election.
The critical question for both Labour and the Tories is this: how do they win a majority in 2015? As it stands Labour are 69 seats short of a majority and the Tories are 21. The polls look good for Labour at the moment, less good for the Tories and terrible for the Lib Dems. But a lot can change between now and the election. With all the uncertainty over the economy, it is difficult to know precisely how things will look in three years time.
What we can be more certain about is which seats the parties will concentrate their efforts on trying to win in 2015. Look at Labour’s top 100 target seats for 2015: 83 are held by Tory MPs, 12 by Lib Dem MPs and five belong to other parties like the SNP. The implication of this is that Labour is going to be locked into a close battle with the Tories.
But look at the Tories' road to a majority in 2015. Of their top 20 target seats, 14 are Labour, while six (30%) belong to Lib Dem MPs. Of their top 50 target seats, 37 are Labour and 13 are Lib Dem (26%). To get a majority with the smallest swing, Labour would need to win something like 56 Tory seats, nine Lib Dem seats, and four seats from other parties. Only 13% of the seats they need belong to Lib Dem MPs. The Tories by contrast, need 15 Labour seats and six Lib Dem seats, meaning the Lib Dems account for 26% of the seats they need to form a government.
Another way of looking at this is to consider the proportion of Lib Dem seats that are marginal to Labour and those to the Tories. Unsurprisingly, the same picture emerges: of the 20 most marginal Lib Dems seats 14 are Lib Dem-Tory marginals, compared to just six that are marginal with Labour (of their 10 most marginal seats the ratio is 7 to 3)
So come the general election, the Lib Dems and Tories will not be partners against Labour, but direct opponents of one another. What does this mean for the coalition, and for Lib Dem strategy? The question for the Lib Dems is this: since the Tories will be disproportionately focused on their seats, do they stand a better chance of defending them with a centre-right, pro-government,anti-Labour pitch, or a centre-left, anti-Tory one? More significantly, will they do better by remaining in the coalition until 2015, or by leaving earlier and developing a clear and distinct pitch to voters in these critical seats?
There are obvious risks attached to leaving the coalition ahead of 2015 but against these it should be acknowledge that in order to hold Lib Dem-Tory marginals, it is Labour tactical votes that the Lib Dems will have to appeal to. As such it is difficult to resist the view that the longer the Lib Dems remain in a coalition that is increasingly drifting to the right, the harder it will be to reach out to these voters.
David Klemperer is an editorial assistant and Guy Lodge is co-editor of IPPR’s quarterly journal Juncture.