The UK Supreme Court ruled 8-3 that parliament must vote before the government triggers Article 50 of the Lisbon Treaty, removing Britain from the European Union.
On Tuesday morning the President of the court Lord Neuberger read their decision that the government alone does not have the power to "Serve Notice" to the EU.
Serving "Notice" is the process of triggering Article 50, which after the morning's ruling, the government must get an Act of parliament authorising them to do so.
Previously the government had argued it's royal prerogative powers were sufficient. This was rejected in late 2016 by the Divisional Court of England and Wales.
Tuesday's 8-3 decision dismissed the government's appeal.
Each of the three dissenting judges offered their own opinion.
Among its conclusions, the court's judgement stated:
Thus, the referendum of 2016 did not change the law in a way which would allow ministers to withdraw the United Kingdom from the European Union without legislation. But that in no way means that it is devoid of effect. It means that, unless and until acted on by Parliament, its force is political rather than legal. It has already shown itself to be of great political significance.
The court also ruled that the government is not legally obligated to include the devolved administrations in Scotland, Wales, and Northern Ireland in its decision regarding Brexit.