Edinburgh. Britain's departure from the European Union has revived the debate for an independent Scotland, which was thought to have been settled in a landmark referendum nearly six years ago.
Scots voted by a majority of 55 percent to remain part of the United Kingdom in 2014, effectively taking the issue off the table in what was described as a "once-in-a-generation" decision.
But nationalists argue Brexit represents a material change in Scotland's constitutional arrangements with the UK government in London.
Some 62 percent of people north of the border voted to remain in the EU in 2016.
That is now prompting some who voted "no" to independence in 2014 but "yes" to stay in the bloc to shift their attitudes on Scotland going its own way after more than 300 years of union.
"I did vote in the last referendum and I actually voted to remain in the UK," said Christopher Clannachan, who took part in an independence march in Glasgow earlier this month.
"I think the Brexit situation has highlighted a real deficit in the UK's constitution where Scotland votes for one thing and does not see that in return.
"So that's what's changed for me and that's what's changed for a lot of people."
- 'Electoral mandate' -
The First Minister of Scotland's devolved parliament, Nicola Sturgeon, has in recent months been ramping up the pressure for a new independence referendum -- dubbed "indyref2".
Sturgeon wrote to Britain's Prime Minister Boris Johnson after the December general election, at which her Scottish National Party (SNP) won a landslide across Scotland.
But he said London would not transfer powers to Edinburgh to hold another referendum, arguing it would "continue the political stagnation that Scotland has seen for the last decade".
Sturgeon accused Johnson's ruling Conservatives of ignoring the will of the people.
"The problem for the Tories is the longer they try to block democracy, the more they show the Westminster union is not one of equals and fuel support for independence," she wrote on Twitter.
The Scottish government is expected to set out its response and next steps in the coming days.
The stand-off could trigger a legal challenge but experts warn such an approach is unlikely to be successful.
"Whether there is a second referendum -- and if so, on what terms - is a political question that will be resolved in the political arena," the UK Constitutional Law Association assessed in a paper.
"There are no legal short cuts through that space," Chris McCorkindale and Aileen McHarg added in the article, "Constitutional Pathways to a Second Scottish Referendum".
Sturgeon has said the SNP has a mandate for independence based on previous victories in general and Scottish parliamentary elections that have increasingly backed her party.
That has prompted many to point out that it may be prudent for her and fellow nationalists to wait for the next Scottish elections in 2021 to secure more political and moral leverage.
The SNP's leader in the UK parliament, Ian Blackford, has said Conservative cabinet ministers had conceded that "Westminster cannot keep saying 'no' to a second referendum on independence".
He told the Herald newspaper in an interview that Tory ministers have told him privately that "this is a line which is going to be difficult to hold in the longer term."
Nicola McEwen, a professor of territorial politics at Edinburgh University, says if support for a fresh vote grows to a point where it reflects a clear majority, the UK government would likely have to accept.
- Too close to call -
Pro-independence marches are a common sight on the streets of Scotland's main cities of Glasgow, in the west, and Edinburgh, 50 miles (80 kilometres) away in the east.
Earlier this month, an estimated 80,000 people braved icy winds and torrential rain, waving blue and white Saltire flags and calling for an end to "London rule".
But even if London agrees to allow a second referendum, nationalists still face a battle to secure the support of a majority of their compatriots.
Polls over the past year consistently show no clear majority for either side, making any result too close to call.
"There has been an increase (in support for independence) but it has been modest and has been driven primarily by those who voted to remain in the European Union," said McEwen.
Any economic damage from Brexit in the coming years, however, could fuel Scottish discontent and increase the chances of a "yes" vote to independence.