What is the UK Supreme Court?
So, why did the court have the final say on the matter?
What is the Supreme Court?
It is the highest court in the United Kingdom. The judges, known as justices, have the final say on the biggest legal issues and are the ultimate check and balance on the UK's laws and constitution.
The justices only hear the cases that raise what they consider to be a genuinely important point about how the UK's laws should be interpreted and applied - that is about one in three cases referred to it.
It sits opposite the Houses of Parliament, its location symbolising the relationship between the two: Parliament makes the laws and the Supreme Court oversees their fair and just use.
How did the Supreme Court rule against the government on suspending Parliament?
Eleven of the Supreme Court justices - the largest possible panel - heard legal arguments from court cases in England and Scotland.
They had to decide whether judges have the power to intervene in how a prime minister prorogues Parliament. And, if they do, was Edinburgh's court right to conclude Mr Johnson had acted unlawfully in closing it for such a long period?
Their decision was unanimous.
The judges said that Parliament had not been prorogued - the decision to suspend it was null and void.
They said it was for the speakers of the Commons and Lords to decide what to do next.
In response to the ruling, Commons Speaker John Bercow said MPs "must convene without delay".
What other cases end up in the Supreme Court?
The justices hear cases that have been considered in lower courts in any part of the United Kingdom, other than some issues from Northern Ireland and appeals against criminal convictions from Scotland.
There is always an odd number of Supreme Court justices, so that if they disagree on the outcome, there is a clear majority ruling one way or the other.
The court will be 10 years old on 1 October and it has so far heard 835 appeals, including cross-appeals, where a defendant asks a higher court to review a lower court's decision, and linked cases.
Here are some examples:
- Two 2018 judgements meant the police could be sued for compensation, after a 76-year-old woman Elizabeth Robinson was knocked over and when detectives botched a solvable investigation into the John Worboys case
- In 2016, the justices said a law about gang murder had been wrongly interpreted for 30 years
- In 2015 Nadine Montgomery won a 16-year-battle for compensation over brain damage to her son during his birth
- Three years later, justices backed end-of-life decisions
Can the Supreme Court strike down laws?
Only Parliament can pass or cancel laws. The Supreme Court's role is to decide on the correct interpretation of those laws when there is a dispute. If the justices think a law conflicts with human rights safeguards, it can tell Parliament it should reconsider the legislation.
Who appoints Supreme Court justices?
New justices are appointed by the Queen on the recommendation of a panel of legal experts from each of the UK's nations. Applicants must have been a High Court judge for at least two years or a practising lawyer for 15.
Who is Supreme Court president Lady Hale, and who are the other ten Supreme Court justices?
Eleven of the court's justices heard the case against the government.
- Lady Hale is the president of the court and, before she became a judge, she was the architect of the UK's internationally recognised laws on the rights of children. As the first female justice, she has been critical of the lack of female representation on the body in the past.
- Deputy president Lord Reed, a senior Scottish judge, also sometimes sits in the European Court of Human Rights and at Hong Kong's Court of Final Appeal. He previously read the Supreme Court ruling that overturned high employment tribunal fees claiming they prevented access to justice.
- Lord Kerr was Lord Chief Justice of Northern Ireland before joining the Supreme Court at its 2009 opening. As the only Northern Irish justice, he argued for free NHS abortions to be given to Northern Irish women when they travel to England, but the Supreme Court rejected the case.
- Lord Lloyd-Jones is the Supreme Court's judge from Wales and a Welsh speaker. He specialises in international law and even advised the courts in the trial of former Chilean dictator Augusto Pinochet. He also chaired the Law Commission - which advises the government on which laws need reforming - up until 2015.
- Lord Wilson is one of the UK's most experienced judges in family law, having spent 12 years ruling on those cases. In 2014, he made the case for extending same-sex marriage to Northern Ireland, arguing that same-sex marriage strengthened the institution rather than weakened it.
- Lord Carnwath is an expert in company and commercial law and the former Attorney General, or chief legal adviser, to the Prince of Wales. He has a particular interest in environmental law and has attended UN-backed conferences aimed at strengthening legal protections for the environment.
- Lord Hodge is the second Scottish judge on the panel of 12. He specialises in commercial law, in particular intellectual property and land valuation.
- Lady Black is another expert in family law who has taught students at university and, from 2010, also sat as a Court of Appeal judge. She was previously the head of International Family Justice - a body which deals with cross-border family cases.
- Lady Arden was a Court of Appeal judge for 18 years and another former head of the Law Commission.
- Lord Kitchin is an expert in the complex branch of commercial cases that deals with intellectual property, such as patents that protect an invention being copied by a rival.
- Lord Sales is the most recently appointed judge, in January 2019, and his varied career includes sitting in the semi-secret tribunal that adjudicates on complaints against MI5. In 2005, he defended the government's position of not holding an inquiry into the Iraq war and was in the original court which ruled government must ask Parliament before invoking Article 50. This led to the Daily Mail labelling him and the other two judges as "enemies of the people."
The only justice who did not sit was Lord Briggs, who comes from a career as a judge and lawyer in commercial cases.