NICOLA Sturgeon’s top legal adviser has accused the UK Government’s lawyer of being “unfair” and trying to “belittle” the Indyref2 case before the Supreme Court.

In her rebuttal at the close of a two-day hearing, the Lord Advocate strongly criticised the approach of Sir James Eadie KC, who earlier today called her case “strange” and "uncontrolled and surprising".

Dorothy Bain KC said: “Sir James's characterization of what is involved here is unfair. It's just not right. That he should say what he said about why we're here. It’s so unfair.” 

Ms Bain told five justices she referred the case to the Court “responsibly and after careful consideration as to whether it was appropriate to do so”.

She said: “As I hope would be obvious to this court, the reference has been brought, not because the issue is trivial or one that has been raised on a whim, or 'willy-nilly' as one of the phrases that was used yesterday [had it]. It is a matter of the utmost constitutional importance."

The Court has been asked to consider whether Holyrood could stage Indyref2 under its existing powers, or whether that an Indyref2 Bill would “relate to” the Union and the UK Parliament, which are reserved to Westminster and so off-limits to the Scottish Parliament. 

Ms Bain asked the Court to consider the issue in June, after refusing to sign off a draft Indyref2 Bill at Holyrood in case it went beyond Holyrood’s legislative competence.

The 2014 referendum had Westminster’s consent, with the UK Government lending Holyrood the power to stage the vote.

However successive Tory Prime Ministers have refused another transfer of powers, arguing the No vote of eight years ago should stand for a generation.

In June, Ms Sturgeon asked Ms Bain to refer the question of Holyrood holding a unilateral referendum to the Court under an unused provision in Schedule 6 of the 1998 Scotland Act.

Sir James spent most of his time before the Court arguing Ms Bain was not entitled to use this provision in the Act, as another, established mechanism for the Court to consider Holyrood legislation passed by MSPs was intended by Section 33 of the Act.

He suggested that if the Court was to consider a draft Bill it could open the floodgates to a host of other references on hypothetical questions, draggiing the Court into policy making.

Urging the justices to throw out her reference as ill-founded, he called the Lord Advocate’s method “uncontrolled and surprising”.

He asked: “Where is the limit on her case? Suppose the Scottish Government have an early draft of a bill? What if there isn’t a bill at all and they simply have an abstract policy idea?”

He said if there was no limit to what could be referred to the court in this minister, the justices could be asked for a view on an idea “that has just clicked into the head of the First Minister”.

He said the court was “not a talking shop” and there was a risk of it “being dragged at the behest of the the law officers in all the devolved administrations into providing advice”.

On Monday, he had also said the Scotland Act set out "carefully regulated and specific timetable and set of requirements before a reference can be made. You can't just do it willy nilly. It's very carefully done.

"It sets the time point for jumping off at the point where the legislation is in effect final apart from [royal] assent"

In her reply, Ms Bain said Sir James’s argument did not reflect reality, as only government law officers could make such references, and they would naturally act responsibly.

She said the route used to bring the reference had never been done in the 23 years of devolution, and was via a sweep-up or catch-all provision that was intentionally broad, to allow matters of “the broadest amplitude” to be considered.

If Westminster had wanted a more “circumscribed” power in the Scotland Act, it would have made that clear, she argued.

She said: “We do raise legitimate important and constitutionally, crucially important questions for not only Scotland, but for the whole of the United Kingdom. And it's entirely appropriate that this Court, the Supreme Court of this country, deals with this issue.”

She said: “Sir James was suggesting that things were to be done willy nilly, just when something popped into somebody's head, that they would make a reference.

“It’s to belittle, it’s to minimise the enormity of the issue that has been brought to this court. 

“It’s to show that the issue is not academic, it’s crystallised, it is a real issue, a real issue that has been a festering issue since the days of devolution. 

“And in this context, we've taken the responsible, the correct constitutional role in bringing this matter for a reference. 

“And Sir James's characterization of what is involved here is unfair. 

“That's the point I'm making. It's just not right. 

“That he should say what he said about why we're here. It’s so unfair. 

“And it's reflected in everything that we've put forward in our case.

“The trigger is the First Minister of Scotland, because she recognised the importance of the issue and the importance of making sure that everything's done legally, asked that I as law officer of the day  took the consideration as to whether or not a reference was appropriate.

“Now, it may be that a different law officer would take a different approach on a different day.

“But what we know is that in the history of cases that come before this Court, lawyers win cases they think they're going to lose and lose cases they think they're going to win. 

“And when there are very clearly, carefully balanced legal arguments that really can't allow a minister in charge of a Bill to make the positive statement that's necessary in this case, the constitutionally right thing to do for the law officer of the day is to bring this issue to the court. 

“And that's what's been done.”

Lord Reed, the Scottish president of the Court, said the Court’s justices were "most grateful for the submissions received".

He said: “As I said at the outset, we will require time to consider what we have heard and what we will be reading. We appreciate the importance of this and we will let you have our judgement as soon as we can.”

He pointed out yesterday that the justices also have some 8,000 written pages of submissions to consider, and their ruling may take “some months”.

Ms Sturgeon has said if the Court rules Holyrood can proceed with its own referendum Bill, Indyref2 will be on 19 October next year.

If the Court says Westmminster’s consent is required, she has said she will fight the next general election as a “de facto” referendum on independence instead.