The Supreme Court will today begin hearing arguments on a landmark case that will decide whether the government can trigger the process for leaving the European Union without consulting parliament.
Proceedings will last for four days, with a ruling expected to be announced in January.
The government is appealing the verdict of the High Court, which said last month that parliament’s consent was required before the government invoked Article 50.
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Attorney General Jeremy Wright will make the case that the royal prerogative should be used to begin the process of leaving the EU, since the matter has already been put to the people in the EU referendum.
He will say that the High Court’s ruling implies parliament would be able to “micromanage” the negotiations to leave the European Union.
“Suppose that the government wished in the negotiations to preserve for UK citizens one part of EU law rights but not another part – that position could have a direct impact on the continued enjoyment of current statutory rights,” said a paper submitted to the court in advance.
“I think it is such a dangerous road to be going down to be attacking the judges and their integrity and their independence" – Gina Miller
“On the court’s analysis, the government could not adopt that position and reach agreement on that basis without specific approval in an act of parliament. Parliament would be put in the position of ‘micromanaging’ treaty negotiations.”
But lawyers acting for the victors in the High Court case – former investment manager Gina Miller and hairdresser Deir Dos Santos – will argue that triggering Article 50 would inevitably lead to a change in UK domestic policy and therefore should be the preserve of parliamentary consent.
Later in the week, the Scottish and Welsh governments will argue that their parliaments should be required to have their say through a legislative consent motion.
But Wright accused the devolved administrations of asking judges to “stray into areas of political judgment rather than legal adjudication”.
“The court should resist that invitation, particularly where the underlying issue is one of considerable political sensitivity,” he added.
"If the judges go down this road they are placing themselves above parliament. It will create a serious, constitutional issue" – pro-Brexit MP Iain Duncan Smith
In the run-up to the case, attention has turned to the 11 Supreme Court justices who will rule on the matter and their views on the referendum.
Miller said some of the coverage had been “disgraceful”.
“I think it is such a dangerous road to be going down to be attacking the judges and their integrity and their independence,” she told the Guardian.
However, the former work and pensions secretary Iain Duncan Smith, a leading advocate of leaving the EU, said judges should not be able to overrule the will of the people.
He told the Telegraph: “If people aren't careful we will be left with rule making by unelected judges. This is a political matter.
“It is a much more important debate than just Europe. If the judges go down this road they are placing themselves above parliament. It will create a serious, constitutional issue.”
The Supreme Court itself has addressed the controversy in a post on its website, underlining that it is not ruling on whether or not the UK should leave the EU.
“The justices are aware of the public interest in this case and the strong feelings associated with the wider political questions of the UK's departure from the EU (which we stress are not the subject of this appeal),” the statement read.
“The justices' duty is to consider the legal questions impartially, and decide the case according to the law. The range of parties and interveners already before the court is such that the justices are satisfied that all issues and points of view will be represented.”