The UK's top court will on Wednesday rule whether it is legal for Scotland to hold an independence referendum next year without the consent of London.
First Minister Nicola Sturgeon's devolved government in Edinburgh wants to hold a vote in October next year on the question: "Should Scotland be an independent country?"
The UK government, which oversees constitutional affairs for the whole country, has repeatedly refused to give Edinburgh the power to hold a referendum.
It considers that the last one -- in 2014, when 55 percent of Scots rejected independence -- settled the question for a generation.
But Sturgeon and her ruling Scottish National Party (SNP) say there is now an "indisputable mandate" for another independence referendum, particularly in light of the UK's departure from the European Union.
Most voters in Scotland opposed Brexit.
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Scotland's last parliamentary election returned a majority of pro-independence lawmakers for the first time.
At a hearing in the UK Supreme Court last month, lawyers for the government in London argued that the Scottish government could not decide to hold a referendum on its own.
Permission had to be granted because the constitutional make-up of the four nations of the United Kingdom was a "reserved" matter for the government in London.
Lawyers for the Scottish government want a ruling on the rights of the devolved parliament in Edinburgh if London continues to block an independence referendum.
Lord Advocate Dorothy Bain, Scotland's top law officer, said Scottish independence was a "live and significant" issue in Scottish politics.
The Scottish government is seeking to create its own legal framework for another referendum, arguing that the "right to self-determination is a fundamental and inalienable right".
"The question of whether such a poll is within the competence of the Scottish parliament... is an issue that I invite this court to finally resolve," said Bain.
Stephen Tierney, a professor of constitutional theory at the University of Edinburgh Law School, wrote in a recent blog about the case that Scotland's bid to legislate to hold a new referendum would "most likely" be declared to be beyond its powers.
Should that happen, Sturgeon has promised to make the next UK general election, which is due by January 2025 at the latest, a de facto verdict on independence.
Sturgeon's SNP ran in the 2021 Scottish parliamentary elections on a promise to hold a legally valid referendum after the Covid crisis subsided.