What will happen next?
The Supreme Court is set to give its judgement in a legal Battle over Brexit on Tuesday 24 January.
The Supreme Court’s judgement comes after an appeal against the High Court’s rejection of ministers’ arguments.
Theresa May says the government already has the power to invoke Article 50 of the Lisbon Treaty without the say of parliament. She would like to start Brexit talks by the end of March.
However, campaigners say parliament must be consulted before she can go ahead with the plans.