Labour’s 2015 firewall is former Lib Dem voters

With 18 months to the election, the latest skirmish has broken out in the geeks’ war to predict the result. But fun though the battles are, history really is bunk for this one. There is, though, one way we can understand how the war will be won.

The fresh round of the debate was started by a projection by the Oxford academic, Stephen Fisher, that the Tories have a 57% chance of winning a majority, and Labour just 15% chance. In the 28% chance of a hung parliament, he projects the Tories being the largest party 88% of the time.

This contradicts most other projections. Bookmakers currently have Labour as favourites (6/5 at the shortest odds), followed by a hung parliament, and then the Tories on only around 3/1 to win a majority. When I last wrote about 2015, I concluded that past elections pointed roughly towards an electoral tie – which would put Labour as the largest party and just short of a majority.

The trouble is, all these projections (including mine) use past election to predict what will happen in 2015 – and this doesn’t work.

On the one hand, governments tend to lose votes after they’ve served a full term: suggesting Labour should win the election. On the other, oppositions generally lost support as an election gets closer: which, in the context of current polls, suggests the Tories should win.

It’s not hard to see why precedent doesn’t stand up at the moment. The major parties are historically unpopular so there’s not the usual zero-sum game of one gaining at the other’s unpopularity. The coalition confuses three-party switching; and the rise of UKIP has split both the vote of the right and of anti-government protestors. Anyway, as Randall Munro has pointed out, electoral precedents are there to be broken.

So forget using past elections to predict May 2015. Instead, let’s look at how the election will be decided*.

There’s a simple question we can ask, that over time will tell us who’s going to form the next government: what’s happened to the people who voted Lib Dem in 2010?

In the six months after the 2010 election, the Lib Dems’ support fell from 21% (YouGov, May 13th) to 9% (YouGov, November 11th). Labour’s vote intent went from 34% to 40%. Since then, the two parties’ support has stayed roughly at the same level.

Looking at the latest poll of each of the major firms**, about a third of 2010 Lib Dem voters now say they would vote Labour:

With the Lib Dems getting 23% at the last election, this means Labour has gained about 8pts from 2010 Lib Dems. It’s the biggest transfer of votes between any parties – easily eclipsing the loss of Tories to UKIP. So I conclude:

Unless Labour loses these post-2010 Lib Dem defectors, it will win the election. This is Labour’s firewall.

Ok, that needs a couple of strings attached.

Labour got 29% in the last election. Adding 8pts to this gives 37% which is ok but not resounding: it may be enough to give Labour a small majority.

This counts on Labour not losing many of its 2010 voters, which seems likely as it has the best retention rate of the parties. But it will lose some, so they also need to replaced from other places, including 2010 non voters. At the moment, this is happening.

It assumes the Tories can’t improve much on their 2010 vote. Answering that needs more space, but in short I don’t see evidence that they’re currently able to appeal much beyond their 2010 voters. Just getting back to where they were in 2010 would be a challenge and wouldn’t be enough to beat Labour if the Lib Dem defectors stay solid.

This also assumes that the trends are consistent nationally, though in reality, incumbency and tactical voting will change the way individual constituencies behave. But in fact this looks to help Labour more than the Tories. As Mark Gettleson has pointed out, there are a lot of Tory-held marginals where tactical voting for Labour by 2010 Lib Dem voters will give the seats to Labour.

Equally, while the Tories have 19 Lib Dem seats in those they can win with a swing of 4.5pts (compared with 9 Lib Dem seats for Labour to win) – so the Tories benefit more from a Lib Dem collapse – the experience of Lib Dem success in defending their seats suggests that the Lib Dems won’t lose those seats as easily as a uniform national swing calculation would predict.

So, I don’t see how electoral precedent can be used to predict what will happen in 2015. But the path to victory for Labour is clear. For anyone looking at the polls over the next 18 months, the key number is not in the Tory or Ukip columns: it’s how many 2010 Lib Dem voters are now supporting Labour.


* It will really be decided by what the parties say, what the leaders do, what happens to the economy, whether the aliens land before or after the election, and so on. Politics is about ishoos, not blocks of people being marshalled around Excel columns. But this is a blog about public opinion, so I’m looking at the impact of all those things on blocks of voters.

** I’d include others, like Opinium and Survation, but they don’t publish the data for this table.


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