Over at Charlie’s place, two fellows named Tim and Barry raised the old canard that Scottish secession will lead to unending Conservative control of not-as-great Britain. They were unconvinced by (or ignored) the evidence contained in the previous post.
Are they right? After all, U.K. elections are decided using first-past-the-post. National vote shares matter only inasmuch as they translate into victories in individual constituencies. In the United States, for example, Democrats can win the national House vote by almost 2% and still lose the chamber, which is what happened in 2012. Is the U.K. similar?
Short answer: no.
Longer answer: losing Scotland knocks Labor down to 217 seats, versus 306 for the Tories. Parliament shrinks from 650 to 591. That means Labor needs to capture 45 seats to outsize the Conservatives and and 79 to gain an outright majority.
Is that doable? Well, the way to find out is to look at Tory constituencies and ask how much of a swing would be needed to flip the weakest 45 and the weakest 79. If the required swing is huge, then the Tories would indeed have a lock on the 2015 election sans Scotland.
And whaddaya know? The Conservatives are facing at least 82 swing seats. See here and here and here. Translation: It won't take much of a swing to knock the Tories off their perch. The polls are already showing a 7-point swing even if Scotland walks away. If the Liberal Democrats remain the number-three party, then Labor will not a hard time putting together a winning coalition in 2015. The rise of UKIP, of course, is more worrying ... but only if it wins enough seats to put together a majority with the Conservatives.
To sum up: the U.K. parliament is more responsive to the popular vote than the U.S. House of Representatives. Even without Scotland, Labor would be able to win a parliamentary majority as long as it remains ahead in the popular vote. And right now, it is ahead in the popular vote in England and Wales.
This is amateur psephology, of course. I welcome data that shows why the above analysis is wrong. (And I think I now need a British Isles tag.)