
Since its inception after the Constitutional Reform Act (2005) a number of extremely significant judicial review cases have ended up in the UK Supreme Court, the final court of appeal in the UK. Arguably, none are as significant as Miller vs. Prime Minister in 2019. So, what was this case about and why was it so constitutionally significant?
What was the political background to the case?

Parliament had been deadlocked since 2018 on passing a deal to enable Britain to leave the European Union. In January 2019 Theresa May’s Withdrawal Agreement was defeated by 230 votes, the largest parliamentary defeat in modern history and her Brexit deal was subsequently defeated two more times. This led to her downfall as Prime Minister in July 2019 and the succession of Boris Johnson. As Prime Minister Johnson was willing to take a much harder line on Brexit than Theresa May and countenanced (or at least appear to countenance) a No-Deal Brexit. However, many parliamentarians actively sought to prevent a No-Deal Brexit. Johnson, however, wanted to use the ticking clock of Article 50 to force Parliament to accept a deal rather than risk a no deal scenario. Proroguing Parliament would prevent them from being able to pass legislation preventing a no-deal Brexit.
What was Miller vs Prime Minister about?

The Miller vs Prime Minister case surrounded the issue of the prorogation of Parliament. Prorogation is an ordinary parliamentary process in which a parliamentary session comes to an end before a new one can begin. Prorogation is a royal prerogative power – this means that it is not a decision taken by Parliament and is instead taken by the monarch on the advice of the Prime Minister. As it is a royal prerogative power, it also means its exercise cannot be scrutinised by Parliament. However, the decision to prorogue Parliament was made subject to judicial review after being challenged in two key cases – one in Scotland and one in England.
Why was the prorogation in 2019 controversial?
Prorogation is a normal process; it happens regularly in order to allow Parlaiment to reset and begin a new session. However, the circumstances in 2019 were very controversial.

On the 28th of August Johnson advised the Queen, Elizabeth II, to prorogue Parliament. The prorogation would last from the 10th of September until the 17th October, the date of an important meeting of the European Council. Parliament only returned from the summer recess on 3rd September, which would mean there were only five sitting days for business before prorogation. This would be a remarkable long prorogation (it was normally about 10 days, but this would be 34) and was quite abnormal. However, the monarch is bound by strict convention to accept the advice of their Ministers, and therefore Queen Elizabeth II therefore ordered Parliament prorogued.

On the 3rd of September, Parliament had taken control from the government of the order paper. They used this time to pass the EU Withdrawal (No.2) Act which was introduced by Labour MP, Hilary Benn. This bill forced the Prime Minister to send a letter to the European Union asking for an extension to the Article 50 deadline. This would, in essence, remove the immediate threat of a no-deal Brexit that Boris Johnson was hoping to rely on to force through his own deal.
The prorogation of Parliament took place on the 10th of September 2019. It was extremely controversial and led to dramatic scenes in the House of Commons when Black Rod came in to announce Parliament had been formally prorogued:
What were the legal cases that were bought forward?
In Scotland, a case was bought forward by the SNP MP Joanna Cherry and Jolyon Maugham, a prominent anti-Brexit barrister. As a result of the urgency of the case it was taken directly to the Court of Session, Scotland’s highest court. The Court of Session ruled that the issue was non-justiciable because it was a royal prerogative power. However, this was appealed and under appeal the court found that the prorogation of Parliament had been unlawful as the Prime Minister had advised the Queen to prorogue Parliament because he was to attempting to avoid parliamentary scrutiny of Brexit.
In England, as soon as the intended prorogation was announced Gina Miller filed litigation to stop it. Miller has come to public prominence in 2017 during Miller vs Secretary of State for Exiting the European Union (Miller vs Brexit) for preventing the Government of Theresa May being able to use the royal prerogative to trigger Article 50, instead ensuring Parliament took the decision itself. The case went to the High Court, but they ruled that the issue was non-justiciable (that it was not something the courts had the jurisdiction to make a judgement on). Their judgement said:
The constitutional arrangements of the United Kingdom have evolved to achieve a balance between the three branches of the state; and the relationship between the Executive and Parliament is governed in part by statute and in part by convention. Standing Orders of both Houses elaborate the procedural relationship between the Executive and Parliament. This is territory into which the courts should be slow indeed to intrude by recognising an expanded concept of Parliamentary Sovereignty.
Miller, however, immediately appealed the ruling in the High Court and the case was sent to the Supreme Court.
What did the Supreme Court say?

The Supreme Court heard the Cherry and Miller cases together as they were fundamentally surrounding the same issue. Eleven judges (the maximum allowed) sat on the case. They heard the case for three days. The argument from the government was essentially that the issue was non-justiciable, that this was a normal prorogation and therefore the Prime Minister’s power could not be challenged. The claimants argued that the Prime Minister had instigated the prorogation to undermine the ability of Parliament to carry out its fundamental duty to scrutinise legislation and the government, as such, the prorogation could not be lawful in a representative democracy.
On the 24th of September the Supreme Court published its ruling. They unanimously said that the case was both justiciable and that the prorogation was unlawful. They said that the Prime Minister had acted ultra vires in regard to his powers as he had advised the monarch to do something that was unlawful and had undermined both parliamentary sovereignty and representative democracy:
That advice [of the Prime Minister to the Queen to prorogue Parliament] was unlawful. It was outside the powers of the Prime Minister to give it. This means that it was null and of no effect. It led to the Order in Council which, being founded on unlawful advice, was likewise unlawful, null and of no effect and should be quashed. This led to the actual prorogation, which was as if the Commissioners had walked into Parliament with a blank piece of paper. It too was unlawful, null and of no effect…It follows that Parliament has not been prorogued and that this court should make declarations to that effect. We have been told by counsel for the Prime Minister that he will “take all necessary steps to comply with the terms of any declaration made by the court” and we expect him to do so. However, it appears to us that, as Parliament is not prorogued, it is for Parliament to decide what to do next.
The judgement in R (on the application of Miller) (Appellant) v The Prime Minister (Respondent) Cherry and others (Respondents) v Advocate General for Scotland (Appellant) (Scotland)
In the remarkable opinion, that had never been made before, the Supreme Court ruled that the prorogation had no legal effect, and that Parliament should continue as if nothing had happened:
What happened in Parliament following the judgement?
The Prime Minister said that he disagreed with the ruling but would abide by it. On the 25th of September, just a day after the Supreme Court ruling, the Speakers of both houses reconvened them:
Why is this case so significant?
Miller vs Prime Minister was the most significant judicial intervention in the political process since the formation of the Supreme Court in 2009, and perhaps even before that when the highest appellate court was based in the House of Lords. Miller vs Brexit Secretary was a case about where legal power resided over the triggering of Article 50. Theresa May argued that it was a prerogative power and Miller argued it was a power that belonged to Parliament. There was no question that the issue was really justiciable. This case, however, about a prerogative power that was not under dispute. No-one argued that prorogation was not a royal prerogative power. However, it was about whether the exercise of that power had been lawful. It was directly about the limits of an established royal prerogative power. They stressed that the motives behind the decision, and not just the decision itself, were important. Therefore, its precedential effects on the UK’s unwritten constitution are extremely significant.
Could the Government have ignored the verdict?
In the UK parliament is sovereign. In the words of A.V Dicey Parliament “make or unmake any law”. Therefore, Parliament can ignore the rulings of the courts. There have been times when this has happened. Famously, a ECtHR decision to enforce the right of prisoners to vote in the UK was ignored by Parliament. However, a ruling by the Supreme Court is extremely difficult for the Government to ignore. Doing so would risk undermining the Rule of Law which is a fundamental principle of the UK constitution. The fact that prorogation was found to justiciable indicates there are very few limits on judicial review and that the Supreme Court is increasingly willing arbitrate in the political process.
How did the Government react to the verdict in the long-term?
Whatever the courts rule, parliament remains sovereign. This means that Parliament can legislate to change the issue in the future. This is what happened in Ahmed v Treasury and somewhat what happened following the prorogation. In May 2022 the Conservative Government passed the Judicial Review and Court Act (2022). Amongst other things, this Act dilutes the right to judicial review and makes it more difficult in the future.
Article Summary
Miller vs Prime Minister is perhaps the most significant case ever heard by the civil courts in the UK. It saw the judiciary test the right of the Prime Minister to carry out a power that was indisputably within his remit. It showed the UK Supreme Court being willing to involve itself in arbitrating explicitly political issues and in doing so set itself a precedent of judicial activism in the future.
Key Terms
Constitutional Reform Act (2005) – A significant constitutional reform that created the Supreme Court, reformed the role of the Lord Chancellor and created a Judicial Appointments Committee.
No-Deal Brexit – A Brexit that would have seen Britain withdraw from the European Union without signing a deal with the European Union. Many commentators believed that such a Brexit would have been disastrous.
Article 50 – The Article of the Lisbon Treaty that allows a country to give notice that it seeks to withdraw from the European Union.
Royal Prerogative – A number of privileges and powers of the monarch, most of which have now been passed to the Prime Minister and members of the government. For example, the Prime Minister appoints the Cabinet on behalf of the monarch.
Judicial Review – The process whereby the Judiciary considers whether or not the government has acted beyond the law. The process of Judicial Review has grown in importance in recent years. This is largely due to the effects of the Human Rights Act (1998).
European Council – The Executive Body of the EU that defines its political direction.
Prorogation – The mechanism by which a parliamentary session is ended. The Queen prorogues Parliament on the advice of the Prime Minister. In 2019 the prorogation of Parliament was reversed by the Supreme Court in Miller vs. Prime Minister.
Recess – The holidays that Parliament regularly takes. These are usually in line with school holidays.
EU Withdrawal (No.2) Act (Benn Act) – A Private Members Bill passed in 2019 which forced the Government to prevent a No-Deal Brexit.
European Union – The collection of European States that form a collective union in which general political and social standards are accepted, like freedom of movement. It was originally called the European Economic Community, which Britain joined in 1973 and left in 2020.
Ultra Vires – A finding that the government or a government body has acted beyond its power or authority.
Miller v Brexit Secretary – A significant Supreme Court Case that challenged the right of the Government to instigate Article 50 without the explicit approval of Parliament. This case limited the Royal Prerogative powers of the Executive.
Miller v Prime Minister – A Supreme Court case in which Gina Miller challenged the right of Boris Johnson to advise the Queen to prorogue Parliament in August 2019. The Supreme Court ruled that the prorogation had been unlawful.
Ahmed v Treasury – A significant early Supreme Court case involving the freezing of suspected terror supporter’s assets. The judgement was not welcome by the Government and Parliament quickly legislated to make such actions legal. It is therefore an excellent example of both judicial review and parliamentary sovereignty.