Britain’s top court is due to begin hearing arguments on Tuesday on whether Scotland’s semi-autonomous administration can organise an independence vote without the London government’s consent.
Scottish First Minister Nicola Sturgeon plans to hold a new independence referendum in October next year, but the UK government is adamant it won't happen, saying the 2014 referendum -- which was won by the 'no' campaign with 55% of the vote to 44% in favour of independence -- was a 'once in a generation event.'
Since then the numbers have tightened and Scots are evenly split on independence, although they have consistently returned pro-independence politicians to parliaments in Westminster and Edinburgh over the last eight years, with the SNP winning every national vote since then.
The Scottish Parliament currently has a majority of MSPs who are pro-independence from Sturgeon's Scottish National Party and the Greens.
What is involved in the Supreme Court hearing?
Five judges on the UK's Supreme Court in London will hear arguments in this case over the next two days, although a decision is not expected for weeks, or possibly even months.
The British government's position is that only Westminster can give the green light to any new independence referendum because constitutional issues remain the purview of the London government and are not devolved to Edinburgh.
Meanwhile, the Scottish government will say the referendum -- like the 2016 Brexit referendum -- is only advisory and will not in itself mean Scotland becomes independent, as there would need to be negotiations and new laws passed before that could actually happen.
The Scottish National Party will also make a submission to the court about the right of self-determination.
Nicola Sturgeon has said that if her government loses the Supreme Court case, she will make the next UK national election a de facto plebiscite on ending Scotland’s three-century-old union with England.
She did not give details of how that would work. A vote held without the approval of the UK government would not be legally binding.
Sturgeon said that if the courts blocked a referendum, “we put our case to people in an election or we give up on Scottish democracy.”
“It should be a last resort,” she said. “I don’t want to be in that position. I want to have a lawful referendum.”
Sturgeon promised to produce documents in the coming weeks outlining the economic basis for independence and answering questions such as what currency the country would use after a split.
She said her goal of holding a referendum in a year’s time was realistic.
“There’s little point speculating on the outcome of a court hearing, but should that be yes, we have the plans ready to go to legislate,” she said.