Lawyers challenging the government’s right to trigger Britain’s exit from the European Union without a vote in the House of Commons are to invoke a “radical revolutionary tradition” enshrined in Scottish law for more than 300 years.

The Independent Workers Union of GB, which was set up to represent workers in the so-called gigeconomy, has told the supreme court that the government would be in breach of Scottish constitutional law if it were to trigger article 50 without Westminster’s agreement.

The IWGB has hired the constitutional lawyer Aidan O’Neill QC, who has challenged the UK government’s claim that it has the prerogative to trigger article 50 without a parliamentary vote in his submission.

Echoing the Scottish government’s case to the court, O’Neill says that because leaving the EU involves each part of the UK, the court must take account of Scotland’ constitutional law and in particular the Claim of Right Act 1689, signed the year after England’s weaker Bill of Rights was drafted. It codified the “radical revolutionary tradition” in Scotland that a monarch was always answerable to the law and the people, in this case its parliaments, he says.

O’Neill says the court must also take contemporary issues into account, such as the rights of EU migrant workers and trade union members the IWGB represents.

The UK government is expected to vigorously contest these arguments in next month’s hearing, but they add to the increasingly complex legal battle over Brexit.

Theresa May’s government has confirmed it would not be shifting its position on whether article 50 could ever be reversed, despite speculation of a U-turn.



In its skeleton argument (pdf)released last Friday, the attorney general, Jeremy Wright QC, and other lawyers on the government’s legal team state: “Before the [high court] it was common ground between the parties that an article 50 notification is irrevocable and cannot be given conditionally ... [The supreme] court is invited to do the same.”



The Scottish and Welsh governments have already been allowed to take part in the action, which was brought by Gina Miller, an investment manager, and Deir Dos Santos, a hairdresser, increasing the scope of the case.

In a further development on Monday, it emerged that Northern Ireland’s attorney general, John Larkin QC, is now expected now to take part in the hearing, increasing the chances that the cross-border deal with the Republic of Ireland in the Good Friday agreement will also become part of the legal argument.

Mick Antoniw, counsel general for the Welsh government, said the future of the UK’s devolution framework was at stake. “The attorney general for Northern Ireland will appear before this court because he is a party to that claim [which] raises such important issues for the devolution framework in the United Kingdom as a whole,” he said.

Scotland’s chief law officer has also been asked to address the 11 supreme court judges on specific areas of Scottish law that are affected by Brexit. In a brief submission to the court, the lord advocate, James Wolffe QC, said the claim of right made “a unilateral act of the crown” on this issue unlawful.

O’Neill’s submission argues: “The contemporary significance and resonance of this Scottish tradition is clear in the present case. In effect, the Scottish constitutional tradition is not that the crown has plenipotentiary imperial prerogative ‘Henry VIII’ powers unless and until these are expressly limited by parliament.

“Rather the Scottish constitutional tradition is that the crown, the government, only has such powers as are expressly granted to it by the people gathered together in a representative assembly.”

The Scottish government and O’Neill also raise the Sewel convention, a rule introduced at the time of Scottish and Welsh devolution in 1999, which says both devolved parliaments have to approve any act of Westminster that affects their powers.

Wolffe’s submission calls it a convention and so not a legally binding veto, but O’Neill goes further and says that because it is recent legislation, Sewel has legal force. If the supreme court agrees, that would effectively give the Scottish parliament a veto over the Brexit bill.

Aileen McHarg, a professor of public law at the University of Strathclyde, was sceptical about O’Neill’s arguments. She said he was right to argue that Scotland and England historically had different views about a monarch’s privileges, but that was not same as their powers.

O’Neill’s argument that the monarch could only act in this way with the explicit approval of a parliament was very unusual, she said. “This claim is not supported by any authority, and I have never before seen it suggested that there is any difference between Scots and English law in this regard,” she said.

If his arguments were accurate, then nothing done by the UK or Scottish government which uses prerogative powers would be lawful because they had no explicit legal authority to use them, she added.