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Author: Sophie Andrews-McCarroll


On Tuesday, 24 September 2019, 11 Supreme Court judges ruled unanimously that it was unlawful for the Prime Minister to advise the Queen to prorogue – formally suspend – Parliament. They ruled that in the eyes of the law, prorogation never happened and said that it was up to the Speaker of the House of Commons and Lord Speaker to determine the next steps. Shortly after the ruling, the Speaker of the House, John Bercow, announced that Parliament would sit again the following day, Wednesday, 25 September 2019 at 11.30 a.m. The Prime Minister flew back from the United States, where he had been attending the UN General Assembly, in order to address Parliament.

The Supreme Court ruling

When Parliament was prorogued in September, there were three challenges to the lawfulness of the Government decision. One in Scotland, one in Northern Ireland and one in the courts of England and Wales.


The case in Scotland was brought forward by a cross-party group of 75 MPs and one barrister (QC) on 30 July, out of concern that the Prime Minister might attempt to prorogue Parliament with the aim of avoiding debate on Brexit in the lead up to the 31 October Brexit deadline. The first hearing in the Scottish Court found that there were no legal standards against which to judge the legitimacy of the Prime Minister’s decision, and thus ruled in the Government’s favour. This was then appealed to the Inner House of the Court of Session, which ruled on 11 September 2019 that the prorogation was unlawful.

England and Wales

The challenge in the UK court was brought by activist Gina Miller, who was also responsible for the successful challenge in 2016 that the Government should be required to have parliamentary consent before triggering Article 50. She was joined in this by former Conservative leader and Prime Minister Sir John Major. The High Court in England and Wales rejected the challenge and found that the Prime Minister’s decision was political and not justiciable in a court of law.

Northern Ireland

The issue of prorogation was not dealt with directly in the ruling in Northern Ireland, as it was being litigated in England and Scotland.

Supreme Court

The decisions in both Scotland and England were appealed to the UK Supreme Court. On 17 September, the UK Supreme Court heard a joint appeal from the judgement of the High Court and the Inner Session. The hearings lasted until 24 September, when the President of the Supreme Court, Lady Brenda Hale, gave the Court’s judgement.

In her statement, Lady Hale emphasised that the judgement was about only whether the advice given by the Prime Minister to the Queen on 27 or 28 August, was lawful. The court also considered the legal consequences if it was not.

The court first considered whether the lawfulness of the Prime Minister’s advice is justiciable: whether the Prime Minister’s actions could be subject to legal challenge. In doing so, the court examined two questions: firstly, the extent to which prerogative powers – such as the power of the Prime Minister to advise the Queen to prorogue Parliament – exist, and if so to what extent. Secondly, the extent to which the exercise of prerogative power can be subject to judicial review.

What is prerogative power?

Prerogative powers are unique to the sovereign in constitutional monarchies such as the UK, in that they are technically exercised by the Monarch. In practice, however, they are exercised by the Queen or King of the day only on the advice of her or his ministers. As the UK Constitution is unwritten, there are no formal texts as to what constitutes prerogative powers. They have been defined as “a collection of special powers, rights and immunities vested in the Crown that is not conferred by Parliament.”[1]

The Supreme Court decision considered the extent to which the Courts have jurisdiction to decide on the limits of prerogative power and concluded that in this case, they had jurisdiction to determine the limits of the power of the Prime Minister to advise the Queen to suspend Parliament.

What did the Court rule?

The Court found that “there is no doubt that the courts have jurisdiction to decide upon the existence and limits of a prerogative power.” Thus, the court decided that what it was considering came down to the limits of the power of the Prime Minister to advise the Monarch to prorogue Parliament.

It considered two principles of the UK Constitution: Parliamentary sovereignty, the idea that everyone must abide by the laws that Parliament makes, and Parliamentary accountability, the idea that the Prime Minister and Cabinet are accountable to Parliament. The Court considered that Parliamentary sovereignty would be undermined if the Prime Minister used prerogative powers to prevent Parliament from exercising its sovereignty. The court therefore determined that a decision to advise the Monarch to prorogue Parliament would be held unlawful if it was found to frustrate Parliament, without reasonable justification, in carrying out its constitutional functions.

It did not, therefore, consider the lawfulness of the Prime Minister’s motive or purpose in doing so, only the effect of his decision: the question as to whether or not Parliamentary sovereignty and accountability had been undermined.

The Court found that prorogation had the effect of frustrating or preventing the ability of Parliament to carry out these constitutional functions without reasonable justification and as a result, ruled the prorogation unlawful. It said that it was not a normal prorogation in the run-up to a Queen’s Speech and that the prorogation did prevent Parliament from executing its constitutional function for five out of eight weeks between the summer recess and Brexit day on 31 October.

The legal effect of this, the Court found, was that any prorogation resulting from the unlawful advice of the house “was null and of no effect”. This meant that in the eyes of the law, Parliament was never prorogued. The Court left it to the decision of the Speaker of the House of Commons and the Lord Speaker to determine the next steps. Shortly afterwards, John Bercow, the Speaker of the House of Commons announced that Parliament would sit the following day at 11.30a.m.

What is the significance of the ruling?

As outlined in this Institute for Government blog, the ruling was the first of its kind and has far-reaching consequences for the unwritten UK constitution, in particular the balance of power between the executive, legislature and the judiciary. The Supreme Court ruling consolidated Parliament’s constitutional role, and in particular, the idea of Parliamentary accountability. Where before Parliament’s role in protecting citizens from arbitrary exercise of executive power was performed by Ministers appearing before the House of Commons to answer parliamentary questions, scrutinising and voting on legislation etc., this might have been considered to be protected only through convention and common practice.[2] This ruling ensures that parliamentary sovereignty and accountability is part of the constitutional law of the United Kingdom. If the courts consider it is under threat, they may move to protect it. This is a significant development in the UK constitution: the courts have consolidated executive accountability to parliament in law.[3]


Parliament has not been recalled, rather it is sitting in the same session, as though prorogation had never happened. This means that the Bills which were dropped on 10 September 2019 can continue their passage through Parliament. This also means that the Speaker is unlikely to allow MPs to vote on the Withdrawal Agreement again in its current form, as he previously said that “substantively the same motion” could not be voted upon again in the current Parliamentary session.

Next steps

Before Parliament was suspended, MPs passed a bill, known as the Benn Bill, mandating the Prime Minister to seek an extension to Article 50 if MPs had not approved a Withdrawal Agreement in a meaningful vote by 19 October, the day after the European Council. Boris Johnson has repeatedly stated that he is highly unwilling to do this, and despite his claims that he has been negotiating a new deal, European Commission sources have said that they have yet to see legally operable alternative solutions to the Northern Ireland backstop and have called for more substantial proposals from the UK.

Should the Prime Minister negotiate a new Withdrawal Agreement with the European Union before 19 October, the timetable for legislating for its implementation is tight. The House of Commons must approve the new agreement in a meaningful vote, and then it must be legislated for and implemented before 31 October. The parliamentary arithmetic will be difficult; it seems unlikely that Labour will support a new deal, preferring instead to leave Boris Johnson to request a new extension and then seek a General Election.

The Benn Bill requires that if the Prime Minister succeeds in securing a deal with the EU, a Cabinet Minister must table a motion approving the new deal by 19 October. If this succeeds, the deal must be legislated for in time for an orderly exit on 31 October. If the motion does not pass, there must be a motion approving a no-deal outcome. If this is defeated, the Prime Minister must request an extension to Article 50 from the European Union.

In his opening address to the House, Boris Johnson called for the opposition to support a General Election. However, it seems unlikely that Labour will do so unless he complies with the Benn legislation and requests an extension after 19 October.

It has been suggested that the group of cross-party MPs who succeeded in passing the Benn legislation in early September, could call a vote of no-confidence in the Government and form a caretaker Government with a different Brexit strategy. The leader of the SNP in Westminster, Ian Blackford, has said that he would support a caretaker Labour Government, with Jeremy Corbyn as a temporary Prime Minister. However, the Liberal Democrats have said that they will not, and it is unlikely that the group of former Conservative ministers, who were deselected in the last vote on the Benn bill would support Jeremy Corbyn as Prime Minister.

It is possible that the Liberal Democrats could support a caretaker Labour Government with a different leader, if all parties could agree on a unifying alternative Prime Minister. The purpose of this Government could be to extend Article 50 long enough to get the UK through a General Election or possibly a referendum.


The Supreme Court ruling had a profound effect, not only on the immediate political situation in the UK, but on the constitutional balance of power between the executive, legislature and judiciary more broadly. As the House of Commons sits again, it is on the clear understanding that the judiciary will protect parliamentary sovereignty and accountability. This provides important context when considering the options ahead of MPs in the coming months; whether the Prime Minister agrees a new deal or does not, MPs could have the ability to avert or abet no-deal. The Benn bill demonstrated the potential for cross-party consensus earlier in September, however in the fragmented political climate, doing so again will be far from straightforward.


[1] Alder, J( 2005) Constitutional and Administrative Law, 5th Edition, Palgrave MacMillan, London. P. 305

[2] Raphael Hogarth, The Supreme Court has fortified Parliament’s constitutional role – and its own, Institute for Government, 25 September 2019.

[3] Raphael Hogarth, The Supreme Court has fortified Parliament’s constitutional role – and its own, Institute for Government, 25 September 2019.