The focus of much opinion polling is on the short-term. Has support for this party or that party gone up or down since last month? Which leader’s popularity is increasing, whose is on the wane? Is there any evidence of swing towards or away from independence since the last time the question was asked?

As a result, perspective can be lost. In the hunt for today’s headlines, politically and socially significant long-term changes in the balance of public opinion can be obscured from view. Sometimes it is good to stand back and take the long view.

That is what we do today in a report that looks at the long-term evolution of support both for independence and for the SNP since the creation of the Scottish Parliament in 1999. It is based on data from the Scottish Social Attitudes (SSA) survey. Conducted annually by ScotCen Social Research, this survey attempts to identify changes in the climate of public opinion rather than the latest variation in the political weather. In so doing it has maintained the only measure of attitudes towards how Scotland should be governed that has been asked on a regular basis since 1999, as well as having asked people for whom they voted at each and every Scottish and UK election since then.

The report underlines just how different the political landscape is now from what it was in the early years of devolution. Then, support for independence stood at between 26% and 30%. Indeed, even as recently as 2012, as few as 23% chose independence as their preferred constitutional option in response to the question that SSA has asked each year. Now, in the most recent survey, conducted between July and December last year, twice as many (46%) backed independence as did four years previously. Indeed, for the first time more people supported independence than devolution, which secured the backing of just 42%. (Meanwhile 8% did not want any kind of Scottish Parliament at all.)

In short, the research makes clear that the September 2014 independence referendum left an important long-term legacy – a much higher level of support for independence than ever before. The increase has been particularly marked amongst younger people, with potentially important implications for future trends in support for independence, and amongst those with a strong sense of Scottish identity.

All in all, while the No side may have won the September 2014 referendum, it was the Yes side that won the campaign. As a result, far from proving to be ‘decisive’ the independence referendum left Scotland more divided on the constitutional question than ever before. And that, of course, is a key reason why the country is now potentially facing the prospect of another independence referendum rather sooner than once had seemed likely.

Not only is support for independence now much higher, it also seems that people’s views on the subject are more likely to be reflected in how they decide to vote. Back in 2001, just 35% of those who then supported independence voted for the SNP in that year’s UK general election. Even in 2010 the figure still stood at no more than 55%. But in the 2015 contest, in which the SNP secured 56 of Scotland’s 59 seats, no less than 85% did so.

A similar, albeit less dramatic, trend is also in evidence in Scottish Parliament elections. In 2003 only 58% of those who supported independence voted for the SNP. By 2007 the figure had already increased to 80%, and more or less remained at that level in 2011, when the SNP won an overall majority at Holyrood. What in fact helped to deliver the nationalists their 2011 majority was the support of nearly two in five (38%) of those who wanted Scotland to remain in the UK. But that latter figure has not been matched again – only around a quarter (24%) of those who want to stay in the UK voted for the SNP last year.

In short, on both sides of the argument how people vote at election time now matches more closely their views on the independence question, suggesting that the second long-term legacy of the referendum was to raise the importance of the issue in voters’ minds. And thanks to the substantial increase in support for independence, one consequence in turn has been to enable the SNP to become the dominant party in Scottish politics.

Now the party is minded to try and call another referendum in the wake of the outcome of the EU ballot in which 62% of Scots voted to Remain but the UK as a whole voted to Leave. However, it is far from clear that holding a second independence referendum with a view to enabling Scotland to escape the alleged deleterious consequences of a ‘hard Brexit’ will provide the SNP with the best of circumstances (from its perspective) in which to revisit the issue.

First, as previous surveys have shown, the issue of EU membership divides supporters of independence. According to the latest SSA survey, one in three (33%) of those who say they would now vote Yes to independence report that they voted last June to Leave. There is thus a risk that a referendum campaign that tied independence to being a fully paid up member of the EU could cost Yes the backing of some of these supporters.

Second, despite the 62% vote in favour of remaining in the EU, Scotland is now more Eurosceptic than at any time since the advent of devolution. Back in 2000 just 38% of people in Scotland said that Britain should either leave the EU (11%) or should remain a member but try to reduce the EU’s powers (27%). Almost as many (31%) actually wanted the EU to become more powerful. Now, however, no less than two in three are sceptical about the EU, with 25% saying that Britain should leave and no less than 42% that it should try to reduce the EU’s powers.

This means that over half of those who voted to Remain –  56% – did so despite wanting the EU to be less powerful. Amongst those Remain supporters who say they support staying in the Union the figure is even higher – 65%. In short, much of the Remain vote appears to have been an unenthusiastic one, and their regret at leaving the EU may not be sufficient to persuade them that Brexit is a good enough reason to change their minds about staying in the UK.

The SNP now hopes to be able to embark on another independence referendum. It does so against a much more favourable backdrop from its perspective than in 2012 when agreement was reached between the Scottish and UK governments about the holding of the ballot that took place in September 2014. Doubtless, it hopes to profit from the legacy of increased support left by that original ballot. But ‘banging on about Europe’ could prove less fruitful in winning over those who previously voted No to independence than the outcome of the EU referendum in Scotland might lead one to expect.

About the author

John Curtice is Professor of Politics at Strathclyde University, Senior Research Fellow at ScotCen and at 'UK in a Changing Europe', and Chief Commentator on the What Scotland Thinks website.