The likely explanation emerging for the Liberal Democrat vote share in the general election coming in much lower than even the immediately previous polls suggested is that there was a late swing away from the party, partly due to Lib Dem supporters being less willing to turn out (see, for example, this from ComRes). It’s natural to slide from that into a general story about the party peaking after the first TV debate and then being in decline during the rest of the campaign.
However, there is a risk of missing the wider context – and is show by these figures from a post-election Greenberg Quinlan Rosner poll. Looking at when people say they made up their mind how to vote, we find support for the Liberal Democrats as follows:
Before election called: 18%
Shortly after election called: 29%
After first debate: 60%
After last debate: 26%
Last couple of days: 26%
On election day: 28%
The Conservative Party peaked in the first two categories and Labour peaked in the “after last debate” category, suggesting that although Gordon Brown overall rated poorly in that debate he did manage to rally the core vote.
It’s the 18% figure for those who decided how to vote before the election was called that turned out to be the problem for the party. There was a debate surge and decline, but getting 28% amongst those who decided on polling day would have still put the party in close contention for second place – were it not for the deadweight from the people who had decided before the election started.
The poll also sheds some light on the class patterns to vote. Liberal Democrat support was up 4 points amongst ABs, up 2 points amongst C1s but down 5 amongst C2s and up 1 point amongst DEs. Labour support was also down amongst the C2s, but support for Conservatives and others was sharply up. (These figures are comparing two different polls, so remember the margins of error.)
This growth in C2 Conservative support may help explain the failure to squeeze the Conservative vote in some key seats if those campaigns relied too much on trying to squeeze the Conservative vote by targeting up-market parts of the constituency.