The UK Supreme Court is to be asked to rule on the competence of the Scottish Parliament legislating for a non-binding referendum on independence, in advance of a bill being taken through its parliamentary stages.

First Minister Nicola Sturgeon had been expected to announce legislation which would face a court challenge after its passage through Holyrood, but made the surprise move when confirming to the Parliament on Tuesday that the Scottish Government intends to hold the referendum on Thursday 19 October 2023.

The UK Government has refused to make an order under s 30 of the Scotland Act 1998 to permit a referendum with binding effect, as was done ahead of the first referendum in 2014, but Ms Sturgeon said the issue of independence "cannot be suppressed". She continued: "It must be resolved democratically. And that must be through a process that is above reproach and commands confidence."

The proposed referendum would be "consultative, not self-executing", but would have the same question as before on the ballot paper – "Should Scotland be an independent country?" – and, she claimed, would have the same status as the 2014 vote.

Ms Sturgeon said the Lord Advocate had agreed to make a reference of the provisions of the bill to the Supreme Court, which would be done that afternoon. A provision of the Scotland Act allows for competency to be tested in this way, though the question has been raised whether the court would regard the question as premature when the bill might be amended during its passage.

The court later confirmed that the reference had been received, and that the first step will be for it to be referred to the President of the Court, Lord Reed for directions. "He will decide whether there are preliminary matters to be addressed, when the case will be listed (heard), how many Justices will consider the reference, and which Justices will sit on the bench. At this stage, we cannot confirm when the case will be heard."

Most legal commentators consider the court unlikely to rule the bill as within competence, having regard to the trend of recent decisions, but the First Minister said that if it did not, the next general election would be a "de facto referendum. Either way, the people of Scotland will have their say”.

Opposition parties accused the First Minister of using the referendum proposal as a distraction from pressing issues facing the country and the Government's record on these.

Murray Etherington, President of the Law Society of Scotland, commented: "Any bill for a further independence referendum needs to be legally clear and command the confidence of parliaments, governments, and people. It also needs to deliver a fair test and decisive expression of views of the people of Scotland.

"The provision of a new s 30 order would put the competence of the bill beyond doubt. If there is no s 30 order, there will be a lack of clarity and certainty about the legality of the legislation. These are issues which the courts would have had to decide on, so the Lord Advocate’s referral to the Supreme Court offers an opportunity to address and resolve these key questions."