Today the UK High Court handed down a ruling preventing the UK government from triggering Article 50 TFEU – the EU legislation triggering the start of the administrative procedure for the UK’s exit from the EU - without parliamentary approval.
Following the referendum on 23 June 2016, where the UK voted to leave the EU, Prime Minister Theresa May and the UK government announced that they would use the Crown’s prerogative powers to trigger Article 50 as early as March 2017. The use of prerogative powers would allow the government to trigger Article 50 without the approval of the UK parliament. Claimants argued that the government’s position had no basis in law, in particular under the UK’s European Communities Act 1972 and that the government’s position was contrary to fundamental constitutional principles of sovereignty of parliament.
Ruling in favour of the claimants, the High Court found that the government does not have the power under the Crown’s prerogative to give notice pursuant to Article 50 for the UK to withdraw from the EU, meaning that any trigger of Article 50 requires parliament to vote on the matter. As a result, pending appeal, any decision to trigger Article 50 will require approval by MPs in the House of Commons, as well as approval by the House of Lords.
Following the ruling, the government has confirmed that it will seek to appeal the judgment to the UK Supreme Court. A hearing before the Supreme Court could take place as early as December.
The High Court ruling has important implications for the “Brexit” process. In particular, it gives the parliament an important role to play in the process. With a majority of MPs having voted against Brexit in the referendum, the outcome of a vote to trigger Article 50 cannot be certain. Having said that, MPs will not want to be seen as going against the will of the people and outright opposition to the triggering of Article 50 seems unlikely. Instead, the practical effect is likely to be that the government will have to engage with and at least to some extent agree with parliament on the priorities of the UK’s Brexit negotiation with the EU. This, in turn, may cause delay, increase uncertainty (as to timing and outcome) and will inevitably intensify the public debate about the UK’s role outside the EU and the meaning of “Brexit”.
 R(Miller and others) v Secretary of State for Exiting the EU  EWHC 2768 (Admin)