Chief Justice Robert Reed said the five judges were unanimous in the verdict, delivered six weeks after lawyers for the pro-independence Scottish administration and the Conservative UK government argued their cases at hearings in London.
Scottish Prime Minister Nicola Sturgeon said she was disappointed but would “respect” the verdict. But she said on Twitter: “A law that does not allow Scotland to choose its own future without Westminster approval exposes as myth any notion of Britain as a voluntary partnership and justifies (independence).”
Independence supporters plan to rally outside the Scottish Parliament in Edinburgh and elsewhere on Wednesday.
The semi-autonomous Scottish government wants to hold a referendum next October with the question “Should Scotland be an independent country?”
The UK government in London is refusing to approve the vote, saying the issue was settled in a 2014 referendum in which Scottish voters rejected independence by a margin of between 55% and 45%.
However, the Independence government in Edinburgh wants to change that decision, arguing that Britain’s exit from the European Union – which was opposed by the majority of Scottish voters – has radically changed the political and economic landscape.
Sturgeon argues that he has a democratic mandate from the Scots to hold a new secession vote because there is a majority in the Scottish Parliament that supports independence.
During High Court hearings last month, Dorothy Bain, the Scottish government’s highest legal officer, said most Scottish lawmakers were elected on the basis of a commitment to hold a new independence referendum. She also said the referendum would be advisory rather than legally binding – although a ‘yes’ vote would create a strong impetus for Scotland to break away.
British government lawyer James Eadie argued that the right to hold a referendum rested with the British Parliament in London because it was “crucial for the whole of the United Kingdom” and not just for Scotland.
The Supreme Court judges agreed. They said it was clear that “the bill which provides for a referendum on independence – to end the sovereignty of the UK Parliament over Scotland – has more than a loose or consistent connection to that Parliament’s sovereignty.”
Reed stressed that the court “has not been asked and cannot be asked to give its opinion on the political question of whether Scotland should become an independent country”.
Polls suggest Scots are roughly evenly divided on independence – and also that a majority of voters do not want a new referendum any time soon.
Scotland and England have been politically united since 1707. Scotland has had its own parliament and government since 1999 and sets its own public health, education and other policies. The UK-wide government in London controls matters such as defense and fiscal policy.
Sturgeon said if her government lost the court case, she would make the next UK national election a de facto plebiscite on ending Scotland’s three-century-long union with England. She did not provide details on how this would work.