Landmarks in law: the Brexit court ruling that thwarted Boris Johnson

It’s not often that a case about constitutional news grabs the attention of the public. But in September 2019, more than 30 million people tuned in to watch the proceedings live on the Supreme Court’s website as 11 justices unanimously ruled that the prime minister had “unlawfully” prorogued parliament for five weeks in the run up to the 31 October Brexit deadline.

Not only did the case lead to a general election, it also changed the law. Catherine Barnard, professor of EU law and employment law at the University of Cambridge, says: “Constitutionally, [the case] was hugely significant. The justices knew that, which is why they sat with 11.”

In the case that introduced many people to terms like “prorogation” and “justiciable”, the Supreme Court had to consider appeals in two cases brought in two jurisdictions of the UK.

One was brought by the businesswoman Gina Miller to appeal the English High Court’s decision that the issue was political and therefore not “justiciable” – that’s to say, not a matter for the courts to consider.

The other case was brought by Scottish National Party MP Joanna Cherry QC, and around 70 other parliamentarians. Scotland’s highest civil court had ruled that the issue was justiciable and that the prime minister had acted unlawfully, overturning an earlier ruling from the Scottish High Court.

The Supreme Court, led by Lady Hale, judged the matter to be justiciable on the grounds that for centuries the courts had “exercised a supervisory jurisdiction over the lawfulness of acts of the government”.

The court had to look at the use of prerogative powers, which are exercised by ministers on behalf of the Crown. As Steve Peers, a professor of EU, human rights and world trade law at the University of Essex, explains, the case was about the limits on a prerogative power. “Those limits were set by two constitutional principles: parliamentary sovereignty (meaning that the executive should not use the prerogative to prevent parliament from exercising legislative power), and parliamentary accountability (the capability of parliament to supervise the executive).”

Adam Wagner, a barrister at Doughty Street chambers, suggests that the concept of “parliamentary accountability” was a new constitutional principle, “which gets to the heart of what parliamentary sovereignty is for: accountability to the people.”

The court ruled that the suspension “had the effect of frustrating or preventing the ability of parliament to carry out its constitutional functions without reasonable justification”, which it said was an “improper purpose” for prorogation.

Because the court decided suspension was unlawful, it quashed it. In effect, the court said that parliament had not been prorogued, and left it up the speakers of the two houses to decide what to do next. Parliament sat again the next day.

Former government lawyer Carl Gardner says the case changed the law. “It is unlawful to use prerogative powers in a way that ‘stymies’ parliament – at least unless ministers have a good reason for doing so.” But he adds: “You can’t accuse the judges of activism. It’s the government’s unprecedented use of prorogation that brought this new but understandable precedent from the court.”

And the decision has wider, long-term significance. “It indicates that the courts are prepared to step in if they believe that the use of executive power could pose a fundamental threat to parliamentary democracy,” says Gardner.

Barnard, meanwhile, says it “demonstrates a shift towards the court becoming a constitutional court, through no choice of its own. It has to deal with the cases that come before it.” With that move, she says, comes the risk for the court that there will be a call for parliamentary scrutiny of the judges who sit there.

Wagner adds that there is “an inherent instability” in this change in the court’s role since the UK has no written constitution. “It may be that if and when the UK leaves the EU, this issue can be revisited,” he says.


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