The High Court ruled this morning that the government cannot trigger Article 50 of the Lisbon Treaty without a vote in favour by Parliament.
Theresa May had said that she intended to activate Article 50, formally notifying the EU of the UK's intention to leave, by the end of March 2017.
In upholding the application brought against the government by Anti-Brexit campaigners, the High Court has held that the government does not have power under the Crown's prerogative to start the process of leaving the EU without a vote by Parliament.
The Lord Chief Justice criticised the government's arguments describing them as contrary to "fundamental constitutional principles of the sovereignty of parliament".
The High Court have confirmed that this case is suitable to "leapfrog" the appeal process straight to the Supreme Court.
Depending on how quickly the appeal is heard, this case, which is possibly the most important constitutional case of current times, may throw a spanner in the works of the government's proposed timetable for a hard Brexit.