Theresa May’s determination to avoid a parliamentary vote on triggering Brexit will be tested in the High Court on Thursday in what is shaping up to be an unexpectedly tough challenge for the government.
The court battle has been brought about by fund manager Gina Miller and others, including a Spanish hairdresser, who question whether the prime minister is able to start the process of leaving the EU without MPs’ approval of the decision.
Britain’s top legal talent will be on display, with more than 16 QCs and 20-30 solicitors in the High Court.
In the government’s corner is the attorney-general, Jeremy Wright, who was a criminal barrister in Birmingham before becoming a Tory MP. He will appear along with James Eadie QC, first Treasury counsel.
They face a formidable opponent in Lord Pannick, who has acted many of the leading public law cases of the past 25 years and is one of the UK’s most highly regarded advocates, appearing dozens of times in the European Court of Human Rights and the Supreme Court. He is acting for Ms Miller together with the law firm Mishcon de Reya.
Deir Dos Santos, a Spanish hairdresser, will be represented by law firm Edwin Coe and Dominic Chambers QC. Other interested parties, including Grahame Pigney, a British citizen living in France, have used crowdfunding to finance their appeal and will be represented by Bindmans and Helen Mountfield QC.
Lawyers believe the case is finely balanced and it is by no means certain the government will win. The House of Lords constitutional committee recently concluded that it would be “constitutionally inappropriate” and set a “disturbing precedent” for the government to act on the results of the EU referendum without parliamentary approval.
Separately to the legal case, the former attorney-general, Dominic Grieve, has argued that a Commons vote is required as an “established constitutional convention”. The convention, part of the Britain’s uncodified constitution, relates to significant changes to international treaties, Mr Grieve said.
But other experts believe the legal challenge is doomed to fail because courts are reluctant to intervene in the exercise of power in foreign affairs, including treaties. Critics like Sir Bill Cash, a prominent Leave campaigner, have said that the “proceedings of parliament are outside the jurisdiction of the court.”
The case raises questions of significant constitutional importance — not least the extent of so-called royal prerogative, which consists of vestigial powers once derived from the rights and privileges of monarchs to do as they wished.
Britain has an uncodified constitution that consists of laws built up over many centuries, making the arguments around Article 50 less than clear-cut. Some prerogative powers have been handed to government, including foreign affairs and the power to make and break treaties with other countries.
Ms Miller and others bringing the judicial review challenge argue that the Brexit vote was advisory and not legally binding. Ms Miller says the challenge is not about overturning the result but about the process for triggering Article 50: “Our case is very, very simple. It is about the process; how do we create legal certainty?”
The claimants argue that any use of prerogative powers by Mrs May to trigger Article 50 would be inconsistent with a number of the UK’s constitutional statutes such as the Bill of Rights 1689 and the European Communities Act 1972, which brought Britain into the then EC. It would be unlawful for a prime minister to use the royal prerogative to take away rights given by parliament, they claim.
The government argues that Article 50 does not require a vote in parliament and can be triggered by the prime minister as an exercise of prerogative power. It claims that entering into and withdrawing from treaties is a matter for the government and says the courts are “ill-suited” to hear such a case.
“This is of course a political rather than legal argument; those who are in the royal prerogative camp will tend to be Brexiters,” said David Golten, partner at law firm Wedlake Bell. “Those in the parliament camp are likely to be Remainers. As is frequently the case in political arguments, however, the courts have been called upon to adjudicate.”
The case will be heard by three of Britain’s top judges, including Lord Thomas, the Lord Chief Justice of England and Wales.
It is possible that after the case finishes next week they will reserve their decision on the issue and the case could then “leapfrog” to the Supreme Court, the UK’s highest court, in December.
Nicholas Evans, partner and parliamentary agent in the government and infrastructure team at Bircham Dyson Bell, also says the legal process could delay the triggering of Article 50.
“The answer to this question will fill in another part of our unwritten constitution, so the Supreme Court have cleared their diaries for early December to hear the inevitable appeal. If they find that a parliamentary act is needed to trigger Article 50, this will seriously jeopardise the prime minister’s plan to start the process next March,” he said.