LONDON -- The United Kingdom Supreme Court said on Tuesday it would take months to reach a decision on whether the Scottish government can hold a second referendum on independence next year without approval from the British parliament.

Scottish First Minister Nicola Sturgeon, leader of the Scottish National Party (SNP), has said she wants to hold an independence vote on Oct. 19, 2023, but that it had to be lawful and internationally recognized.

British Prime Minister Liz Truss and her predecessor, Boris Johnson, said they would not grant permission for any referendum, saying a 2014 plebiscite, in which Scots rejected ending the 300-year-old union by 55%-45%, was a once-in-a-generation event that should not be repeated.

However, the SNP says the 2016 vote for Britain to leave the European Union, which the majority of Scottish voters opposed, had materially changed the circumstances.

The Supreme Court, Britain's top court with authority over all civil matters across the United Kingdom, is now being asked whether the Scottish government can pass legislation to allow a second referendum without approval from the U.K. parliament in London.

"It's likely to be some months before we give our judgment," Robert Reed, the president of the Supreme Court, said at the opening of two days of hearings, which he said amounted to the "tip of the iceberg" in the case.

Under the 1998 Scotland Act, which created the Scottish parliament and devolved some powers from Westminster, all matters relating to the Union of the Kingdoms of Scotland and England are reserved to the U.K. parliament.

The British government says that means it is clear that it alone can approve any referendum.

However, the SNP, which has dominated Scottish politics for more than a decade, winning the overwhelming majority of Scottish seats in the 2019 U.K. election, says this means the views of Scots are being ignored.

Last year, it promised to hold a second referendum if it was returned to power in elections to the Scottish parliament and it was subsequently re-elected, albeit with the support of the pro-secession Scottish Greens.

Lord Advocate Dorothy Bain, the Scottish government's most senior law officer, told the court in London that it was in the public interest for the Supreme Court to finally resolve whether a referendum could be unilaterally held.

(Reporting by Michael Holden; Editing by Nick Macfie)