The UK Supreme Court has ruled by a majority of 8 to 3 that an Act of Parliament is required to authorise ministers to give Notice of the decision of the UK to withdraw from the European Union.

The Supreme Court considers that the terms of the European Communities Act, which gave effect to the UK’s membership of the EU, are inconsistent with the exercise by ministers of any power to withdraw from the EU Treaties without authorisation by a prior Act of Parliament.

However, the Supreme Court unanimously that devolved bodies could not hold up the process - decisions on foreign affairs are for the UK parliament to decide. 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.

Further, in relation to NI, the Northern Ireland Act, "...gave the people of Northern Ireland the right to determine whether to remain part of the United Kingdom or to become part of a united Ireland. It neither regulated any other change in the constitutional status of Northern Ireland nor required the consent of a majority of the people of Northern Ireland to the withdrawal of the United Kingdom from the European Union."
https://www.supremecourt.uk/cases/docs/uksc-2016-0196-judgment.pdf

As ever, the summary judgement can be viewed on YouTube:
https://www.youtube.com/watch?v=Q6YcixV_0Sc