In her written argument to the Supreme Court, Dorothy Bain QC also said Nicola Sturgeon’s hopes that a second vote on the question of Scottish independence would lead to Scotland becoming an independent country are “not legally relevant”.
She argued the practical effects of passing the independence referendum beyond “ascertaining the views of the people of Scotland” would be “speculative, consequential and indirect” and should not be taken into account.
The written legal arguments, published on Friday, represent the first time the Scottish Government has set out its reasoning for why they believe it is within the power of the Scottish Parliament to legislate for a second independence referendum.
It was announced earlier this week the Supreme Court would hear oral arguments on both whether the reference should be considered at all by the court and the central issue of competency at a hearing on October 11 and 12.
The UK Government has said it remains “very confident” it will succeed in defeating the Scottish Government.
The deadline for written submissions is August 9, in just over two weeks’ time.
The SNP's political opponents said the cost-of-living crisis meant it was the wrong time to be considering a referendum and that Ms Sturgeon’s obsession with independence “must end”.
Central to the Lord Advocate’s argument is the referendum Bill does not relate to the Union – a reserved matter and therefore outwith the competence of Holyrood – on the basis that its ultimate purpose is only to understand the opinion of the Scottish people.
Ms Bain argues: “The limited legal and practical effect of a Bill to hold an advisory referendum can be said to support the view that the ‘purpose’ of such an instrument is to ascertain the views of the people of Scotland and that relates to the Union in only an indirect or consequential way.
"The motivations and wider ambitions of the Scottish Government represent a ‘subjective intention’, which is not to be equated with the objective purpose of the Bill.”
She also argues that due to the Bill not being self-executing, meaning that either the Scottish Government or UK Government would be legally required to abide by its results, it would have “no legal prescribed legal consequences”.
This was the same with the Brexit referendum held in 2016, which the Supreme Court agreed had no legal effect, but did have “great political significance”.
The Lord Advocate, summing up, states: “The legal consequences of the Bill are, relevantly, nil”.
She adds: “It can therefore be argued that the purpose of an advisory referendum such as prescribed in the Scottish Independence Referendum Bill has ‘at best an indirect … or consequential connection’ or ‘short term’ connection, involving some practical impediment or other effect, necessary for it to be outside competence.
"Even if the criteria are limited to whether the purpose has a ‘loose’ or ‘consequential’ connection to the Union, ascertaining the wishes of the Scottish people, with its purely indirect, contingent and speculative consequences for the Union, would be insufficient to satisfy the test.”
The Lord Advocate said she had made the reference to the UK’s highest court “for the benefit of the Scottish Parliament, the Scottish Government and the people of Scotland (indeed, people throughout the United Kingdom).”
Ms Bain added: “Against that background [of SNP electoral victories], and long-standing consensus that Scotland has the right to self-determination, to what extent, if at all, the holding of a referendum relates to a ‘reserved matter’ is a question of fundamental constitutional and public importance.
"Despite the highly charged political context, it is a question of law. It is therefore a question that can only be authoritatively determined by this court.
“The Lord Advocate believes it is in the public interest that clarity be brought to the scope of the Scottish Parliament’s powers in respect of the issue.”
A spokesperson for the UK Government said: “People across Scotland want both their governments to be working together on the issues that matter to them and their families, not talking about another independence referendum.”
The spokesperson added: “On the question of legislative competence, the UK Government’s clear view remains that a Bill legislating for a referendum on independence would be outside the legislative competence of the Scottish Parliament.”
Sarah Boyack, constitution spokesperson for Scottish Labour, did not comment on whether Holyrood had the power to hold a referendum on independence, stating the question was for the Supreme Court to decide.
She said: “The SNP and the Tories have both spent years speculating about a referendum in a bid to stoke division and distract from their failures in government.
“Yet, the fact remains whether or not the government can hold a referendum, it is a complete dereliction of duty to do so while bills are soaring, the NHS is in crisis, and people can’t afford to put food on the table.
“The SNP need to stop trying to tear communities apart and start using the powers they already have to build a better future for Scotland.”
Donald Cameron, the Scottish Conservative constitution spokesperson, described the push for a referendum as “self-indulgent” and the wrong priority.
He said: “We already know the Lord Advocate isn’t confident in the Scottish Government’s own arguments about the legality of the referendum Bill, and SNP ministers didn’t allow her to come to the Scottish Parliament and answer questions from MSPs before the summer recess.
"Nicola Sturgeon’s relentless obsession with trying to break up the United Kingdom must end.
“She needs to stop playing these political games. Ordinary Scots want her fully focused on tackling the global cost-of-living crisis, addressing record high A&E waiting times, and accelerating our post-pandemic recovery.
“Instead, she is typically creating constitutional grievances to deflect from her own record of failure and divide us all over again.”