What about Scotland, Wales and Northern Ireland?
The Scottish and Welsh governments have been given permission to "intervene" in the case. This has been granted because they represent large constituencies of those affected by the court's decision.
Scotland and Wales have devolved governments. They have responsibilities over a range of things, including health and education.
Both governments are focusing their legal arguments on something called the Sewel Convention. A convention is a generally accepted rule of behaviour.
This one recognises that the UK Parliament in Westminster will not usually legislate on devolved matters without the consent of the devolved parliament. It is now part of the Scotland Act 1998, so has statutory force in Scotland.
Both the Scottish and Welsh governments argue that the UK government cannot trigger Article 50 using prerogative powers alone, and that an act of Parliament is needed. That act will affect devolved matters and so the consent of the devolved governments is required.
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Additional issues
The court will also consider issues relating to the rights of particular groups of people, including British ex-pats abroad, foreign workers in the UK and children, who face losing rights when the UK leaves the EU. These points have been raised by a variety of groups.
Will this case mark the end of the legal process?
Yes, on the issue of the authority to trigger Article 50. However, there is a potentially important caveat. All sides acknowledge that once triggered, Article 50 is irrevocable.
But Article 50 itself does not specifically address this issue. Some lawyers and legal academics believe it can be revoked. If the Supreme Court feels that it needs clarification on the meaning of Article 50 and its "revocability" in order to decide the case,
then it is bound to refer the matter to the European Court of Justice, in effect, the EU's Supreme Court.
That would take months and would cause political ructions. The irony of the EU's highest court having any kind of role and influence in determining how the UK exits the EU would be a very bitter one for those who voted Leave.
http://www.bbc.co.uk/news/uk-38183127
