The facts have not yet changed; so I have not yet changed my mind. But they might; and if they do, I will.

In a recent analysis for Prospect I looked at the votes Labour needed to win the next election. On a uniform swing, I estimated that Labour needs a lead of 6 per cent to be the largest party and 13 per cent to win an outright majority. With tactical voting on the same scale as in 1997, the winning posts are 1 per cent and 10 per cent respectively.

Those calculations assumed that the SNP would maintain their recent poll rating in Scotland; Labour, replacing the Conservatives as the second largest party, would gain a handful of seats. Could Nicola Sturgeon’s resignation as Scotland’s first minister make a real difference, not just to Scotland’s politics, but to the coming UK general election?

The most recent polls suggest little change to party support since Sturgeon’s decision to quit. But these are early days, and there are already signs that the contest to succeed her could be divisive. So things may change. And if they do, the operation of our first-past-the-post (FPTP) voting system could make election night even more dramatic than normal.

Plainly, if Labour is able to advance significantly in Scotland, it will affect what happens at the coming general election. Labour has suffered grievously from its collapse in Scotland after 2010. It’s the main reason why Labour has needed a big lead over the Tories in the Britain-wide polls to regain power at Westminster. The more Labour can recover in Scotland, the less daunting its task in England and Wales. As a rule-of-thumb, every five extra seats that Labour gains from the SNP in Scotland reduces by its target for victory at Westminster by one percentage point. So, if Labour wins an extra 15 Scottish seats beyond the seven indicated by recent polls, Labour will become the largest Britain-wide party with around a three-point lead in the popular vote instead of six, and an outright majority with a 10-point lead instead of 13.

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