John Curtice: Independence debate becoming more polarised

The latest annual British Social Attitudes report published on Thursday shows that attitudes towards Scotland's constitutional status have polarised between SNP and Conservative supporters in recent years, and between Remainers and Leavers.

But Scotland is not unique in this respect. A similar process has happened in Northern Ireland - and it is also evident in attitudes in the rest of the UK towards the constitutional status of Scotland and Northern Ireland.

Back in 2011, when the SNP won an overall majority at Holyrood, the Scottish Social Attitudes survey found that only just over half of the party's supporters (54%) preferred independence to devolution or no parliament at all. Many SNP supporters appeared to be looking to the party to defend Scotland's interests within the UK.

But in the most recent survey, conducted late last year, no less than 82% of SNP supporters said they wanted independence. Rather than defending Scotland's interest within the UK, most SNP supporters are now hoping their party can secure Scotland's exit from the UK.

Unsurprisingly, Conservative supporters are near unanimous in their support for the Union. Just 5% back independence, a figure that has not changed since 2011. But thanks to the marked change in the character of SNP support, attitudes towards Scotland's constitutional status are now polarised on both sides of the political divide.

Meanwhile, an even bigger change of attitude has occurred among Remainers and Leavers.

Despite the SNP's vision of independence being one of independence in Europe, before Brexit people's attitudes towards how the country should be governed were unrelated to what they thought about the EU.

While 44% of those who voted Remain in 2016 supported independence at that time, so also did 45% of those who had backed Leave.

Now the position is very different. Support for independence among those who currently back Remain (65%) is nearly three times that among those who support Leave (22%).

That, at 52%, the overall level of support for independence in the latest survey is six points above what it was in 2016 is largely the result of this change of mood among Remainers. And because four in five SNP supporters back independence, it also helps explain why most SNP supporters now back independence.

This development has important implications for the constitutional debate. To persuade voters, unionists do not simply need to defend the Union but also Brexit. Conversely, nationalists need not only to explain the case for being outside the UK, but also that for being part of the EU.

But this development is not unique to Scotland. Like Scotland, Northern Ireland voted in favour of staying in the EU. And it has also witnessed much the same change in the pattern of attitudes towards the country's constitutional status.

According to the Northern Ireland Life and Times survey, in 2010, only a little over half (52%) of those who were then supporting Sinn Féin backed leaving the UK, while over a third (37%) said that Northern Ireland should remain in the UK. Many of the party's supporters appeared to be looking to it to defend the interests of the nationalist community within the framework of the existing institutions.

Now, however, 78% of Sinn Féin supporters wish to leave the UK, while only 10% say Northern Ireland should stay in the UK. Just as most SNP supporters now want Scotland to leave the UK, most Sinn Féin supporters now want Northern Ireland to do so.

Again, Brexit has been important. At the time of the EU referendum, there was majority support in Northern Ireland for staying in the UK among both Leave voters (83% were in favour) and Remain supporters (64%).

Support for the Union among Leave voters is still as high as it was. But now only 37% of Remain supporters want to stay in the UK, while just over half (52%) say Northern Ireland should leave.

And it is this shift among Remain supporters that accounts for the rise in support for leaving the UK among Sinn Féin supporters (four in five of whom oppose Brexit) - and for the fact that among voters as a whole, support for unification with the Republic now stands at 30%, compared with 19% in 2016.

As in Scotland, the constitutional debate in Northern Ireland is no longer just about the UK Union but about the European Union too.

Indeed, Brexit appears to be influencing attitudes towards the Union in the rest of the UK too. According to the British Social Attitudes survey, in England 35% of Remain supporters say that Scotland should become independent, whereas only 19% of Leave supporters take this view.

Meanwhile, although across Britain as a whole, 62% of Leave supporters believe that Northern Ireland should remain part of the UK, among Remain supporters only 41% do so, while 48% support reunification.

Brexit may be 'done', but it has now become an integral part of the debate about the future of the Union, not just in Scotland but across the whole of the UK.

John Curtice is Senior Research Fellow at NatCen Social Research