The UK Supreme Court today reaffirmed the decision of the High Court in November, confirming that the Government cannot rely on its historic prerogative powers to launch the Article 50 process to withdraw the UK from the EU.

During the case, the Government reiterated its central argument that it could rely on historic 'prerogative powers' (traditionally used to conduct international relations and to make and unmake international treaties) to invoke the Article 50 notification, whilst the respondents argued that the executive act of triggering Article 50 would ultimately overrule an Act of Parliament, the 1972 European Communities Act, a result contrary to the principle of parliamentary sovereignty.

Both parties also repeated the view that once the Article 50 notification had been made, it could not be revoked. This legal interpretation may be subject to a separate challenge lodged in the Irish High Court which questions the revocability of Article 50, a case that could potentially be referred to the European Court of Justice.

The Supreme Court verdict means that the Government should seek Parliamentary approval before starting the two-year negotiating process to withdraw from the EU. This places significant emphasis upon the proposed 'Brexit plan' that the Government offered to MPs in order to secure their approval for the PM's Brexit timetable in December. It is unlikely that this will delay the triggering Article 50, given the political importance of Brexit, with the PM likely to call for an expedited Bill which is expected to be published in the coming days.

The judgement is available in full via the Supreme Court website.

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