Image copyright Getty Images Image caption Scotland voted to stay in the UK by 55% to 45% in the 2014 independence referendum

Support for Scottish independence has reached its highest-ever level in an annual academic study.

But the Scottish Social Attitudes survey also suggested the popularity of the European Union had fallen.

The researchers said this suggested focusing on EU membership may not be the best way to swing more voters towards independence.

The survey has asked the same question about how Scotland should be governed every year since 1999.

It was carried out by ScotCen Social Research and has been published two days after First Minister Nicola Sturgeon confirmed she wants to ask the UK government for permission to hold a second referendum on Scottish independence.

Ms Sturgeon says the Brexit vote has left Scotland at a crossroads, with an independence referendum needed to allow the country to choose which path to take.

But pro-UK opposition parties argue that another referendum will cause further division and uncertainty, and is not wanted by the majority of people.

What are the latest polls saying?

The survey comes as two polls look at the Scottish independence question.

The Scottish Daily Mail's poll of 1,019 adults, which was carried out between 8-13 March, suggested that when "don't knows" are discounted, people in Scotland would vote 53% to 47% to stay a part of the UK.

The Times Scotland's poll of 1,028 adults, which was carried out between 9-14 March, suggested that when "don't knows" are discounted, people in Scotland would vote 57% to 43% to stay a part of the UK.

ScotCen Social Research author Prof John Curtice said you should not compare his survey to the latest polling commissioned by newspapers.

He explained: "The Scottish Social Attitudes Survey is not a short term opinion poll. This was a survey that was done for the whole of the last six months of last year and it is not about trying to measure the short term variation in the weather, which the two polls out this morning try to do, but rather to look at the long term change in the climate."

A key suggestion in the ScotCen survey was that the September 2014 referendum had left a "legacy of dramatically increased support" for independence.

And it said the pro-independence movement looked certain to enter a second referendum campaign in a much stronger position than it had enjoyed ahead of the first referendum.

Asked to choose between independence, devolution and not having any kind of Scottish Parliament at all, 46% of the 1,237 people surveyed between July and December of last year now backed independence.

This is a higher level of support for independence than at any time since 1999 and double the level registered by ScotCen in 2012, when the last independence referendum campaign initially got under way.

Image caption Support for independence since 1999

The Social Attitudes Survey suggested the increase in support for independence in recent years has been most marked among younger people.

As a result, there is now a very large age gap in support for independence, with 72% of 16-24 year olds wanting to leave the UK compared with just 26% of people aged 65 and over.

Independence is now the single most popular constitutional option, with 42% supporting devolution, while only 8% of those surveyed do not want any kind of Scottish Parliament at all.

However, even although Scotland voted to remain in the EU by 62% to 38% in last year's referendum, the survey suggested scepticism about the institution is now at the highest level ever recorded by ScotCen.

Two in three (67%) either want Britain to leave the EU (25%) or for the EU's powers to be reduced (42%).

In 2014, the figure stood at just over half (53%), while in 1999 only 40% of people in Scotland could be considered Eurosceptic.

This scepticism is even common among those who voted last year to remain in the EU, the report concluded, with a majority (56%) of all Remain voters believing the EU should have fewer powers.

Those who currently back independence are also divided in their views about Brexit, with a third voting to leave the EU in last year's referendum.

Their support could be at risk if independence is linked firmly to EU membership, the report's author Prof John Curtice said.

Image caption Levels of euroscepticism in Scotland since 1999

Prof Curtice said the pro-independence campaign had never been stronger electorally in Scotland.

He added: "From its perspective, the outcome of the EU referendum appeared to be a perfect illustration of their argument that for so long as it stays in the UK, Scotland is always at risk of having its 'democratic will' overturned by England.

"However, the commitment to the EU of many of those who voted to Remain does not appear to be strong enough that they are likely to be persuaded by the outcome of the EU referendum to change their preference for staying in the UK.

"Meanwhile, there is a risk that linking independence closely to the idea of staying in the EU could alienate some of those who currently back leaving the UK.

"Nicola Sturgeon might have been wiser to have stayed her hand, for on current trends there is a real possibility that demographic change will help produce a majority for independence in the not too distant future anyway."

'Isolated Britain'

The pro-independence SNP and Scottish Greens welcomed the survey's findings, with SNP MSP Bruce Crawford arguing it was "no surprise" that more people now apparently backed independence given the "systematic unpicking" of promises made after the 2014 referendum by the UK government.

Scottish Greens MSP Ross Greer said voters in Scotland deserves a choice between being "trapped in the angry, isolated Britain planned by the Tories" and "putting our future in our own hands".

But Adam Tomkins of the Scottish Conservatives said the report showed there was already "significant division" in Scotland over the constitutional question, and that another referendum would only make that worse.

And Scottish Labour MP Ian Murray said Scotland "must not be divided again by the SNP's obsession for a second independence referendum".