By a majority of 8-3, the Supreme Court holds that the Government cannot trigger Article 50 notice to leave the EU without Parliament authorising that course by Act of Parliament.
The European Communities Act 1972, s 2 authorises a dynamic process by which EU law becomes a source of UK law and takes precedence over all domestic sources of UK law, including statutes. So long as the 1972 Act remains in force its effect is to constitute EU law as an independent and overriding source of domestic law. It operates as a partial transfer of law-making powers, an assignment of legislative competences, by Parliament to EU institutions, unless and until Parliament decides otherwise.
The fact that withdrawal from the EU would remove some existing domestic rights of UK residents also renders it impermissible for the Government to withdraw from the EU Treaties without prior Parliamentary authority.
On the devolution issues, unanimously the UKSC holds that there is no requirement for the consent of the devolved administrations in giving Article 50 notice. The devolution Acts were passed by Parliament on the assumption that the UK would be a member of the EU, but they do not require the UK to remain a member. Relations with the EU and other foreign affairs matters are reserved to UK Government and Parliament, not to the devolved institutions. Withdrawal from the EU will alter the competence of the devolved institutions, and remove the responsibilities to comply with EU law.
Helen Mountfield QC, Jessica Simor QC, Rhodri Thompson QC and Aidan O’Neill QC (Scot) were involved in this case.
 UKSC 5 Judgmenthttps://www.supremecourt.uk/cases/docs/uksc-2016-0196-judgment.pdf
Court's Press Summaryhttps://www.supremecourt.uk/cases/docs/uksc-2016-0196-press-summary.pdf