The Supreme Court has ruled that an Act of Parliament is required before the UK Government can issue an 'Article 50 notice' to leave the EU.  The Supreme Court, by an eight to three majority, confirmed the High Court judgment issued at the end of last year.

The Supreme Court ruled that issuing the Article 50 notice will result in a fundamental change to the UK's constitutional arrangements by cutting off the source of EU law.  This requires parliamentary legislation.  It will also remove rights conferred on UK citizens, which requires parliamentary authority.  However, the Supreme Court confirmed that the devolved nations do not have a veto over the UK's decision to leave the EU.

The judgment has enormous constitutional significance, though may not change the ultimate shape of a Brexit.  

There is a question as to whether it will affect the Prime Minister's plan to issue the Article 50 notice by the end of March.  The government is expected to publish a Brexit bill as soon as tomorrow in order to try and stay on track.  It remains to be seen how long the parliamentary process will take and what conditions, if any, may be attached to parliamentary approval.