Following the referendum on the UK’s membership in the EU held on June 23, 2016, Prime Minister Theresa May confirmed that her government would initiate the process of withdrawing from the EU by the end of March, 2017, without holding a vote in Parliament. This decision prompted a legal challenge.
On November 3, 2016, a three-judge panel of the High Court of Justice unanimously ruled that the government must obtain Parliament’s consent before it can trigger the formal process of withdrawing from the EU, pursuant to Article 50 of the Treaty on the European Union.
The government argued that it had the authority to withdraw from treaties without seeking parliamentary approval under the “royal prerogative,” the executive powers derived from the monarch under the UK’s unwritten constitution. The High Court rejected this argument on the grounds that the European Communities Act, the statute through which Parliament enabled EU law to have direct effect in the UK, had created enforceable rights for individuals under UK domestic law. The High Court concluded that only Parliament, not the government, has the authority to enact changes in the law that would alter rights established under duly enacted domestic legislation.
The government appealed the High Court’s ruling to the UK’s Supreme Court. A panel comprised of all 11 Supreme Court justices heard oral arguments in early December on an expedited basis. On January 24, 2017, the Supreme Court handed down its eagerly anticipated judgment.
By an 8-3 majority, the Supreme Court dismissed the government’s appeal and upheld the ruling of the High Court on the question of parliamentary sovereignty, stating that “the government cannot trigger Article 50 without an act of Parliament authorizing that course.” The Court’s holding will become a landmark precedent in the field of British constitutional law.
David Davis, the Secretary of State for Exiting the EU, announced that the government will abide by the Supreme Court’s decision and introduce a bill “within days” authorizing the government to notify the European Commission of the UK’s intention to withdraw. Even though the government’s majority is small, it is extremely unlikely that Parliament will refuse to pass the bill.
Nevertheless, members of opposition parties and even some members of the governing Conservative Party, are likely to offer amendments to the bill that will place constraints on the government’s negotiating position, potentially requiring it to maintain the UK’s participation in the EU’s single market and customs union. Other amendments could require Parliament to approve the withdrawal agreement before it can take effect or force the government to reopen negotiations with the EU if Parliament rejects the terms of the deal.
The government did prevail in a parallel challenge to Brexit brought under the Northern Ireland Act, which asserted that the Northern Ireland Assembly, or the people of Northern Ireland, must consent to any change in the UK’s relationship with the EU. This challenge was supported by the Scottish government. Scotland and Northern Ireland, two of the UK’s four constituent nations, each have devolved legislatures that are responsible for education, health, and other matters within their respective jurisdictions. Both Scotland and Northern Ireland voted in favor of remaining in the EU.
The 11 Supreme Court justices unanimously rejected the devolution argument, holding that the devolved legislatures in Northern Ireland, Scotland, and Wales cannot exercise a veto over the decision to withdraw from the EU because authority over the UK’s foreign relations is a reserved power that may be exercised only by the UK government and the national Parliament in London.