SCOTLAND’S most senior law officer, the Lord Advocate, has won his legal battle to go before the Supreme Court in London next month and argue “strongly” that the Scottish Parliament must give its consent before Article 50 can be invoked by the UK Government.

James Wolffe QC will state that Theresa May’s Government simply starting Brexit via Article 50 would “circumvent the requirement for the UK and Scottish Parliaments to address whether, under existing constitutional conventions the consent of the Scottish Parliament should be sought for those changes”.

Under those “constitutional conventions”, the Scottish Government maintains that legislative consent by the Holyrood Parliament is required for actions such as Article 50 being invoked – it is generally recognised that the Scottish Parliament would vote heavily against Article 50, potentially throwing the UK Government’s whole approach to Brexit into even more chaos.

The Supreme Court yesterday granted permission for the Scottish and Welsh Governments to intervene in the Article 50 case brought by businesswoman Gina Miller and others. It was their successful challenge to the prime minister’s plans for triggering Article 50 using the Royal Prerogative instead of a vote in Parliament which the UK Government is appealing against.

A senior Scottish Government source confirmed last night that the Lord Advocate would “strongly make the case on a legal basis” that Holyrood “must have a say” on Article 50.

In another development, the Lord Advocate will argue that triggering Article 50 in the way that Prime Minister May wants would be a breach of the 1707 Act of Union itself.

Article XVIII of the Treaty of Union states that “no alteration be made in laws which concern private right, except for the evident utility of the subjects within Scotland”.

It is likely that the exact nature of “private right” and “evident utility” will be considered by the 11-judge Supreme Court when it hears the case over four days early next month.

The Lord Advocate will also argue that triggering Article 50 using the Royal Prerogative is unlawful because it would “result in a fundamental alteration of the constitutional arrangements of the United Kingdom, including the constitutional arrangements applicable to Scotland, by removing it from the EU and by effecting a significant change in the current devolution settlement”.

Brexit would “result in the people of Scotland (including UK citizens resident in Scotland and EU citizens from other member states resident in Scotland) and Scottish businesses losing rights and freedoms which they currently enjoy” and “result in changes to the powers and functions of the Scottish Parliament and Scottish Government under existing constitutional arrangements by reason of the devolution settlement contained in the Scotland Act 1998”.

The Lord Advocate’s remarks in his submission to the Supreme Court yesterday echo what First Minister Nicola Sturgeon said earlier this month: “The Scottish Government is clear that triggering Article 50 will directly affect devolved interests and rights in Scotland.

“And triggering Article 50 will inevitably deprive Scottish people and Scottish businesses of rights and freedoms which they currently enjoy.

“It simply cannot be right that those rights can be removed by the UK Government on the say-so of a Prime Minister without parliamentary debate, scrutiny or consent.”

Two other groups, The “Expat Interveners, George Birnie and Others” and The Independent Workers’ Union of Great Britain were also given the right to intervene in the case.

In the first hearing, the High Court refused to deliberate on Act of Union 1707 submissions made by Helen Mountfield QC on the grounds that their prior decision that the Government’s actions were unlawful rendered such considerations unnecessary.

A source close to the case stated: “The very fact that they are willing to listen to the Lord Advocate put forward the Scottish Government’s submissions means that the whole devolution argument will have to be heard and considered.”

The Minister for UK Negotiations on Scotland’s Place in Europe Michael Russell said: “We welcome the decision of the Supreme Court to allow the Scottish Government to intervene in the case, however we continue to call on the UK Government to drop the appeal and to accept that Parliament has the right to determine the triggering of Article 50.

“We recognise the decision of people in England and Wales to support Brexit, but the views of people in Scotland cannot simply be brushed aside.”

Mick Antoniw, counsel general for Wales, said the Article 50 hearing raised “issues of profound importance” for the devolved nations.

He said: “This case is not about whether the UK leaves the EU or not. The people have voted for the UK to leave the EU, and the UK will leave.

“The sole legal question is whether the UK government can, as a matter of constitutional law, use the prerogative powers to give notice of withdrawal from the European Union.”

At a meeting of EU leaders in Berlin yesterday, Theresa May said: “We stand ready to trigger Article 50 by the end of March 2017 and I want to see this as a smooth process, an orderly process, working towards a solution that’s in the interests of both the UK and also in the interests of our European partners.”

A UK Government spokesman said the application to intervene by the Scottish and Welsh Governments was “a matter for the Supreme Court.”

He said: “The UK government’s position remains the same, and we will be taking strong legal arguments to court next month.”