A step in the right direction

From the "Summary of the judgment of the Divisional Court", R (Miller) v Secretary of State for Exiting the European Union...

"The question

"1. The issue before the court is whether, as a matter of UK constitutional law, the Government is entitled to give notice of a decision to leave the European Union under Article 50 by exercise of the Crown's prerogative powers and without reference to Parliament. This is a pure question of law. The court is not concerned with and does not express any view about the merits of leaving the European Union: that is a political issue.

[...]

"Conclusion

"10. The Court does not accept the argument put forward by the Government. There is nothing in the text of the 1972 Act to support it. In the judgment of the Court the argument is contrary both to the language used by Parliament in the 1972 Act and to the fundamental constitutional principles of the sovereignty of Parliament and the absence of any entitlement on the part of the Crown to change domestic law by the exercise of its prerogative powers [...]. The Court expressly accepts the principal argument of the claimants [...].

"11. For the reasons set out in the judgment, we decide that the Government does not have power under the Crown's prerogative to give notice pursuant to Article 50 for the UK to withdraw from the European Union."

Or, in other words, the Government cannot trigger Article 50 without the express approval of Parliament.

Sources:

https://www.judiciary.gov.uk/judgments/r-miller-v-secretary-of-state-for-exiting-the-european-union/ [accessed 03 November 2016]

https://www.judiciary.gov.uk/wp-content/uploads/2016/11/summary-r-miller-v-secretary-of-state-for-exiting-the-eu-20161103.pdf [accessed 03 November 2016]