The opinion published is the first of two legal documents to inform the Scottish independence debate. The second, to be published in the coming weeks, is from an advocate and will deal with domestic law and how the Supreme Court “ignored the Scottish constitutional tradition of popular sovereignty”.

Professor McCorquodale has been an advocate before the International Court of Justice (ICJ) and is an expert member of United Nations working groups.

The opinion claims that “the Supreme Court was mistaken in law in its approach to the right to self-determination of the people of Scotland in the Scottish Referendum reference case” and “sets out the main parameters of the right to self-determination in international law” and how these apply to the people of Scotland.

Professor McCorquodale concludes: “In my view, the Supreme Court was mistaken in law in relying on the decision in Reference re Secession of Québec as it did. It was mistaken in its lack of appreciation of the context of the Canadian case, where a referendum had already occurred and was not found to be unlawful, the relevant constitutional principles requiring a government to negotiate with a part of its State that was seeking to exercise its right to self-determination by secession, and whether the case was applicable at all to the structure of the UK. Each of these factors were of relevance to the Scottish Devolution Reference case.”

He adds: “The Supreme Court relied on a statement by the UK government which was not supported by the ICJ in the Kosovo Opinion. The Supreme Court also failed to take into account the reasoning or conclusions of that Opinion. As a consequence, it can be argued that the Supreme Court was mistaken in law in not correctly applying the relevant international law. Further, relying solely on a submission by the UK government to the ICJ might be considered unreliable as evidence in relation to the right to self-determination in international law.”

Mr Hanvey said: “The UK Supreme Court contend that a Scottish government may not exercise a democratic mandate handed to them by the People of Scotland to hold an independence referendum. Whilst within the limited constraints of devolved legislative competency that may be technically accurate, the judgement went further than technical application of domestic law on devolution.

“And this is something that simply cannot be tolerated. There was a suggestion in that judgement that, somehow, Scotland as a nation does not possess the political or legal capacity to exercise its right to self-determination. In suggesting that, the London Supreme Court overturned what has been the accepted legal, historic and political position that the UK is a voluntary Union.

“The right of a people to self-determination is a cardinal principle of modern international law as set out in the UN Charter. As this legal opinion states; peoples, based on respect for the principle of equal rights and fair equality of opportunity, have the right to freely choose their sovereignty and international political status with no interference.

“The legal opinion we have published reinforces and supports equitable access to the right to self-determination of all peoples within the current Union. They also offer robust challenge to the legally flawed judgement of the UK Supreme Court.”