Since the Scottish independence referendum, the Scottish National Party has seen its membership treble and its poll ratings climb. This boost to pro-independence forces after their referendum failure departs from the script established in previous referendums on autonomy or independence. After the failed 1979 referendum on devolution (due to a turnout requirement – the measure got a majority of votes), the SNP fell back in the polls. After the successful 1997 referendum, the SNP gained in the polls, even though devolution was a Labour-implemented project. After the 1980 and 1995 failed referenda, the Parti Quebecois declined a bit in the polls.

So what’s going on? The biggest reason for the SNP’s gains may be that “Yes” and even some “No” voters in the referendum want to make sure that the Westminster parties follow through on their pledges for even greater devolution. Alex Salmond once said, “It’s only SNP votes that concentrate the minds of Labour.”

To a point, the logic makes sense. The British parties are contesting for power at the center, and party leaders are unlikely to devolve power away from themselves if they can at all help it. A credible secession threat is useful for eliciting concessions.

At the same time, though, there has to be some positive incentive for the central government to decentralize, according to my research. If Holyrood becomes a wholly owned subsidiary of the Scottish nationalist movement (SNP plus Greens), then Labour has less reason to give them more power. One of the big reasons Labour was willing to implement devolution was that they could expect to hold power in Wales and Scotland most of the time. In fact, if devolution comes from anywhere, it may come from the Tories as part of a package ensuring “English votes for English laws” (Conservatives are much stronger in England than elsewhere).

Scots supporting more autonomy might do best to vote SNP in Westminster elections and Labour in Holyrood elections, the exact opposite of the pattern typically shown in the polls.(*)

(*) By the way, anti-EU British voters would also do better to vote UKIP at Westminster than in EU Parliament elections: UKIP can’t do anything about Britain’s role in the EU in Brussels, but they can in Westminster. Again, this is the opposite of the pattern that actually obtains in elections.