In 2010, Britain was swept by Cleggmania. Off the back of a highly successful air campaign, the Lib Dems attracted new voters up and down the country. Unfortunately for them, they mainly did so in seats where they had no prospect of success and they actually lost seats to the Conservatives, falling back from 62 seats to 57 seats.
So the Lib Dems had a substantial vote share in the Conservative/Labour marginals where the next election will be decided. Much attention has been placed on this group. The Lib Dems have declined sharply in the polls and these votes will play a big part in the outcome of the next election.
First things first, how many of them are available to be snaffled by rivals? As I noted yesterday, Lord Ashcroft found that they had declined in the 32 most marginal Conservative/Labour seats by just over half, matching the decline in the national opinion polls. In seats where the Lib Dems are not seriously campaigning, it seems that they may lose votes in proportion to their national loss of vote share. This isn't going to be precisely accurate, but uniform national swing clearly doesn't work when we're looking at such dramatic falls in support, so I propose using that.
In those same 32 most marginal Conservative/Labour seats, the Lib Dems averaged 17.5% of the vote. So on average this puts 9 or 10% of the vote in play, regardless of other voter movements. That's a big chunk. In some constituencies, the numbers in play will be substantially bigger.
How these voters have divided between other parties is unclear - different polls have different findings. Those that have expressed a preference are dividing 2 or 3 to 1 in favour of Labour over the Conservatives, with a non-trivial number going to UKIP. Anything up to 40% of these voters still don't know how they are going to vote.
Putting these movements into a typical seat, we find that of our 17.5% Lib Dem vote share, Lib Dem don't knows comprise 7% of the electorate, Lib Dems comprise 5%, Labour 3 or 4% and the Conservatives 1% or so. So there has been a swing to Labour on these voters alone of 1 to 1.5% of all voters (probably closer to 2 to 2.5% of decided voters). And that's without taking account of any other improvements in Labour support or declines in Conservative support from the last election. This is a big bonus.
Because of this effect, much attention has been paid to the Lib Dem to Labour switchers. Are they likely to return to the fold? In short, no. All the polling (and anecdotal evidence) suggests that this group comprises the most zealous supporters of Ed Miliband, matched only by an intense dislike of the Conservatives in particular. I shall look separately at vulnerabilities in Labour's vote, but there's no vulnerability here. These voters are going to be trooping out next May to vote Labour and will be in danger of pushing the pencil through the ballot paper in their vehemence when they mark the cross. If these voters do not vote Labour, it will to inflict maximum damage on the Conservatives. A decline in the number of Lib Dem to Labour switchers would not be good news for the Tories: it would mean that Lib Dem incumbents were likely to do better.
There's a big betting point here. The bigger the Lib Dem tally at the last election, the more of an in-built swing we can expect to see to Labour in Conservative/Labour marginals. I have prepared the following table of Conservative defence seats where Labour are in contention. I have added a column where I have notionally allocated a net 25% of the Lib Dem vote tally to Labour, and ordered the seats in order of the notional majority on that basis. This equates to half the Lib Dem voters switching, and doing so in the ratio 3:1 Labour: Conservative. I'm open to debate on the exact figures, but this seems a fair starting point to me:
Where I have put "MAJORITY" in block capitals, Labour would have taken the seat. So Labour would have won a further 26 seats on this basis. That would have been enough to have made them largest party at the last election.
It will be apparent from this table that some seats are seriously mispriced. It repays very careful study. On this basis, I would rather back the Conservatives to keep Enfield North where Labour need only a 1.91% swing but only 12.2% of the electorate voted Lib Dem in 2010 than backing them to keep Northampton North where Labour need a 2.41% swing but 27.9% of the electorate voted Lib Dem in 2010. Yet the Conservatives are 11/4 in Enfield North and 5/4 in Northampton North. These odds are in the wrong order. There are many similar examples.
And of course, this is just from the starting point of the last election. Labour will hope to gain other supporters and to see the Conservatives fall back. However, I suggest this table makes a more reliable guide to the starting point for the next election than looking at the unadjusted results last time around.
In my next post, I shall draw the threads together and try to establish some principles for handling the sharp drop in the Lib Dem vote when considering these markets.