The UK Supreme Court’s ruling last Wednesday has, at least temporarily, scuppered the prime minister’s plans to limit parliamentary debate before the looming Brexit deadline. Some of the prime minister’s allies have attacked the ruling as a ‘constitutional coup’. But a close reading reveals that the court has stayed within its remit to interpret, rather than make, the law.

In a carefully reasoned judgment, the court emphasized that the case was not about Brexit. But the judges certainly did not shy away from the extraordinary nature of the matters before it, noting that such factual situations have ‘never arisen before and are unlikely ever to arise again… But our law is used to rising to such challenges and supplies us with the legal tools to enable us to reason to a solution.’

The key question before the court was whether the prime minister’s decision to seek prorogation was ‘justiciable’ – i.e. amenable to being reviewed by a court. The English and Scottish courts earlier on in these proceedings had come, dramatically, to opposing views on this.

The Supreme Court was not dissuaded by the inherently political considerations involved in the prime minister’s decision, stating that while ‘courts cannot decide political questions, the fact that a legal dispute concerns the conduct of politicians, or arises from a matter of political controversy, has never been sufficient reason for the courts to refuse to consider it’.

The court went on to emphasize that the Crown’s remaining prerogative powers (exercised on the advice of the government or directly by ministers) have long been subject to judicial scrutiny; such oversight is essential to guarding the separation of powers underpinning the UK’s constitution.

So far, so conventional. The full bench of the Supreme Court was required to grapple, though, with a prerogative power that had never been tested before in the courts. And so they delved back to the 1611 Case of Proclamations: ‘the King hath no prerogative, but that which the law of the land allow him’. In the court’s view, the legal issue to be resolved was the scope of the power to prorogue (the existence of this particular prerogative not being in dispute).

With no case law available to provide direct guidance on this question, the court, instead, relied on two fundamental principles of the UK’s constitution – parliamentary sovereignty and parliamentary accountability. What would be the logical consequence of an unlimited power to prorogue? The ability to shut parliament permanently.

The conclusion: this particular prerogative power had limits. The court held that:

‘A decision to prorogue Parliament (or to advise the monarch to prorogue Parliament) will be unlawful if the prorogation has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions as a legislature and as the body responsible for the supervision of the executive. In such a situation, the court will intervene if the effect is sufficiently serious to justify such an exceptional course.’

Having come to this conclusion, the court was left to examine what justification had in fact been given, noting that the prime minister’s motives were irrelevant. It noted that no clear reason had been given – the relevant documents were all concerned with preparing for the Queen’s speech.

Noting evidence on normal practice for such preparations, including from a former prime minister, the court found it ‘impossible… to conclude…that there was any reason – let alone a good reason – to advise Her Majesty to prorogue Parliament for five weeks’.

The court’s decision was neither inevitable nor a radical departure from legal tradition. It represents the gradual evolution of the long-established legal principle that the crown’s powers are set by the law and supervised by the courts.

Courts have traditionally been reticent to rule on prerogative powers which are ‘high politics’ by nature – classic examples include declaring war and negotiating treaties. In recent years, though, the judiciary has shown a growing confidence to grapple with the contours of those prerogative powers that remain. Deference is still shown when looking at how those powers have been used as opposed to the limits of the prerogative in question.

The Supreme Court ruling won’t reassure those who worry about the emergence of an activist court willing to wade (improperly) into the political arena. Nor will it necessarily bring comfort to those anxious about an unwritten constitution in an era where political conventions are fast unravelling.

But divisive court rulings are nothing new, nor are ministerial outbursts about inconvenient judgments. In the current environment, politicians should take particular care not to send mixed messages which undermine the independence of the UK’s judiciary. Public trust in British institutions is dangerously low and the UK can ill-afford further damage to its reputation as a country steeped in democracy and the rule of law.

The UK Supreme Court’s ruling last Wednesday has, at least temporarily, scuppered the prime minister’s plans to limit parliamentary debate before the looming Brexit deadline. Some of the prime minister’s allies have attacked the ruling as a ‘constitutional coup’. But a close reading reveals that the court has stayed within its remit to interpret, rather than make, the law.

In a carefully reasoned judgment, the court emphasized that the case was not about Brexit. But the judges certainly did not shy away from the extraordinary nature of the matters before it, noting that such factual situations have ‘never arisen before and are unlikely ever to arise again… But our law is used to rising to such challenges and supplies us with the legal tools to enable us to reason to a solution.’

The key question before the court was whether the prime minister’s decision to seek prorogation was ‘justiciable’ – i.e. amenable to being reviewed by a court. The English and Scottish courts earlier on in these proceedings had come, dramatically, to opposing views on this.

The Supreme Court was not dissuaded by the inherently political considerations involved in the prime minister’s decision, stating that while ‘courts cannot decide political questions, the fact that a legal dispute concerns the conduct of politicians, or arises from a matter of political controversy, has never been sufficient reason for the courts to refuse to consider it’.

The court went on to emphasize that the Crown’s remaining prerogative powers (exercised on the advice of the government or directly by ministers) have long been subject to judicial scrutiny; such oversight is essential to guarding the separation of powers underpinning the UK’s constitution.

So far, so conventional. The full bench of the Supreme Court was required to grapple, though, with a prerogative power that had never been tested before in the courts. And so they delved back to the 1611 Case of Proclamations: ‘the King hath no prerogative, but that which the law of the land allow him’. In the court’s view, the legal issue to be resolved was the scope of the power to prorogue (the existence of this particular prerogative not being in dispute).

With no case law available to provide direct guidance on this question, the court, instead, relied on two fundamental principles of the UK’s constitution – parliamentary sovereignty and parliamentary accountability. What would be the logical consequence of an unlimited power to prorogue? The ability to shut parliament permanently.

The conclusion: this particular prerogative power had limits. The court held that:

‘A decision to prorogue Parliament (or to advise the monarch to prorogue Parliament) will be unlawful if the prorogation has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions as a legislature and as the body responsible for the supervision of the executive. In such a situation, the court will intervene if the effect is sufficiently serious to justify such an exceptional course.’

Having come to this conclusion, the court was left to examine what justification had in fact been given, noting that the prime minister’s motives were irrelevant. It noted that no clear reason had been given – the relevant documents were all concerned with preparing for the Queen’s speech.

Noting evidence on normal practice for such preparations, including from a former prime minister, the court found it ‘impossible… to conclude…that there was any reason – let alone a good reason – to advise Her Majesty to prorogue Parliament for five weeks’.

The court’s decision was neither inevitable nor a radical departure from legal tradition. It represents the gradual evolution of the long-established legal principle that the crown’s powers are set by the law and supervised by the courts.

Courts have traditionally been reticent to rule on prerogative powers which are ‘high politics’ by nature – classic examples include declaring war and negotiating treaties. In recent years, though, the judiciary has shown a growing confidence to grapple with the contours of those prerogative powers that remain. Deference is still shown when looking at how those powers have been used as opposed to the limits of the prerogative in question.

The Supreme Court ruling won’t reassure those who worry about the emergence of an activist court willing to wade (improperly) into the political arena. Nor will it necessarily bring comfort to those anxious about an unwritten constitution in an era where political conventions are fast unravelling.

But divisive court rulings are nothing new, nor are ministerial outbursts about inconvenient judgments. In the current environment, politicians should take particular care not to send mixed messages which undermine the independence of the UK’s judiciary. Public trust in British institutions is dangerously low and the UK can ill-afford further damage to its reputation as a country steeped in democracy and the rule of law.