The UK’s highest court has been asked to throw out a request to settle the “festering” issue of whether Holyrood can hold a referendum on Scottish independence without Westminster’s approval. The supreme court was told that the attempt by Scottish ministers to win the court’s approval for a referendum bill was “premature” and “theoretical” by Sir James Eadie KC, a senior lawyer acting for the UK government. Eadie was speaking after Scotland’s top law officer, Dorothy Bain KC, urged the court to give Nicola Sturgeon, Scotland’s nationalist first minister, permission to table a bill that would authorise Holyrood to hold that referendum in October next year. Bain, the lord advocate, said the Scottish independence question was of “exceptional public importance to the people of Scotland and to the people of the UK. It is central to a manifesto commitment endorsed by the people of Scotland”. Scottish voters had consistently elected MPs and MSPs who backed independence, she said. The late Lord Mackay of Drumadoon, a former lord advocate and Scottish appeal judge, had correctly described that as a “festering issue” which had to be resolved. Three successive Conservative prime ministers have refused to authorise a second independence referendum after the SNP lost the first one in 2014, arguing that only Westminster has the legal power to approve one under the Scotland Act 1998 that set up the Scottish parliament. Bain said the Scottish government wanted the court’s approval to table a bill that had very limited legal scope because it would simply set out how the referendum would be run. Even though the result had immense political repercussions, she said, its outcome was not legally binding on any government. As such it had no direct legal impact on Scotland’s status within the UK. The supreme court was only concerned with the wording and purpose of the bill, not what politicians might do after it was enacted, she argued. Five judges led by Lord Reed, one of two Scottish judges in the supreme court, who is sitting with Lord Lloyd-Jones, Lord Sales, Lord Stephens and Lady Rose, are sitting for two days to hear arguments about that question from Bain and Eadie. If the court decides it is lawful for Holyrood to hold that referendum on independence – which the first minister plans to stage on 19 October 2023 – Liz Truss, the prime minister, will face the real prospect of presiding over the break-up of the UK. Outside the court in central London, about 10 independence campaigners held a banner reading “let the people decide”. If the court rules against Sturgeon, she is expected to put Scottish independence at the centre of the next UK general election, by arguing Scotland has an inalienable right to decide on its future. Opinion polls show most Scottish voters support that argument, more than independence itself, although only a third of voters want a referendum next year. As he opened the hearing, Reed said it could be “some months” before the court issued its ruling and disclosed it had more than 8,000 pages of legal arguments and supporting documents to read. “This hearing is the tip of the iceberg,” he said. Addressing the court after nearly four hours of legal argument from Bain, Eadie said the lord advocate’s application should fall at the first hurdle. He said the draft bill failed to meet the statutory tests set out in the Scotland Act 1998 which established the Scottish parliament, and by case law, that any bill put to the supreme court had to have been first scrutinised, amended and then approved by MSPs. This bill had not yet been presented to the Scottish parliament, and had none of the necessary supporting documentation. It had no legal status, he said. Courts needed “the maximum degree of certainty” that they were studying the final act of parliament. Bain had earlier told the court that Holyrood should be able to debate and pass the bill because it did not breach the Scotland Act’s bar against passing legislation which dealt with the UK’s constitution. The bill simply dealt with setting up a consultative referendum and its results were not binding on anyone. “The referendum would have no prescribed legal consequences arising from its result,” she said. It was not the court’s role to speculate on the political consequences of the referendum result. The UK government points out that earlier this year Bain had refused to certify the draft bill as legally competent because she “did not have the necessary degree of confidence” it was lawful. Speaking as he opened the hearing, Reed said Bain’s application could be thrown out on the first question alone, on whether it was appropriate to adjudicate on a draft bill. That would leave the central issue of whether Holyrood can legally stage the referendum unresolved – the court may decide to settle that once and for all. Eadie’s submissions will continue on Wednesday.