Party activists should be cheering on UKIP’s rise in the polls. Why? Because a UKIP surge would most likely end up making it easier for Liberal Democrats to win in Conservative marginals. By my reckoning, every 1% on UKIP’s popularity increases the Lib Dem majority over the Conservatives in these areas by about 90 votes. If last weekend’s polling, putting UKIP at 14%, is correct, that gives Lib Dems in Con-Lib marginals about a 1000 vote head start.
Where do these numbers come from? A recent ComRes poll found that, of people who said they were going to vote for UKIP, 33% were ex-Conservative, 15% ex-Lib Dem and 3% Labour. We can plug these figures into the twenty-three Lib Dem seats in the Conservative top 100 target list (ie the most marginal), and figure out what that means for votes. So, for every 1% that UKIP’s vote goes up, we assume 33% of that came from the Conservatives, decreasing their vote, and 15% of that came from the Lib Dems. * The figures in the graph below are an average of the net impact of this on majorities in those 23 seats.
The usual caveats apply when doing this sort of electoral modelling – as Lib Dems know, national trends don’t always apply locally, incumbents make a difference, national opinion polls can sometimes be very dubious. But there does seem to be pretty compelling evidence that UKIP’s rise is going to help Lib Dems in Con/Lib marginals – and, potentially, help quite a lot.
* If anyone would like to have a play around with the numbers, I’ve put the spreadsheet up here. You can adjust the weights of where the UKIP vote came from – I’ve just used the ComRes numbers. The target list was taken from the excellent UKPollingReport website.
* Tom Richards is a Liberal Democrat member in London.