Triggering article 50
Miller demonstrates how an independent judiciary is unafraid of applying constitutional law against a powerful executive, writes Simon Parsons
The case of R (Miller) v Secretary of State for Existing the European Union  UKSC 5 is of great constitutional importance as it concerns the separation of, and who has, constitutional power in the United Kingdom.
The Treaty of Lisbon inserted a new article 50 into the Treaty on the European Union (TEU) enabling a member state to withdraw from the EU in accordance with its constitutional requirements (article 50(1)). In 2016 the British people, in a referendum, voted to withdraw from the EU. Although the result is only advisory because parliament remains sovereign, the House of Commons subsequently passed a resolution calling on ministers to give notice of withdrawal by 31 March 2017.
There is no doubt that ministers can give notice under article 50(2) but the question for the Supreme Court in Miller was whether they do so under the prerogative powers or only with parliamentary authority. The Supreme Court held, by an eight to three majority, that parliamentary authority was required and that was the constitutional requirement mentioned in article 50.
Instead of eight judgments the majority gave one judgment which is very helpful for the reader but it consists of 152 paragraphs. Three justices gave dissenting judgments. Underlying the majority decision is one fundamental constitutional principle namely, unless permitted by legislation, the royal prerogative does not allow ministers to change statute law or the common law. This has been constitutional law since the Case of the Proclamations (1610) 12 Co Rep 74 which was confirmed in the Bill of Rights 1688.
The decision concerned the European Communities Act 1972. This statute makes EU law part of UK domestic law without, in some cases, any further primary or secondary legislation and actually takes precedence over all domestic sources of UK law, including statutes. In constitutional terms this was unprecedented because it represented a reduction in the sovereignty of parliament. That was not fully recognised until the Factortame litigation in the 1990s in which, in effect, the House of Lords set aside a UK statute that was in conflict with EU law. The 1972 Act is the 'conduit pipe' by which EU law is introduced into UK domestic law.
If notice was given using prerogative power then once a withdrawal agreement came into effect or two years expired the 1972 Act would become defunct. Its direction to the courts to apply EU law would be meaningless because that law would no longer apply to the UK. In fact it would be unnecessary to repeal the 1972 Act although the government intends to do so in the Great Repeal Bill. This would amount to changing a statute using prerogative power which breaks the fundamental constitutional principle stated above.
There was nothing in the 1972 Act (or subsequent domestic legislation concerning the EU) which allows the prerogative to be used in this way. The European Union Referendum Act 2015 makes no provision for such an exercise of the prerogative. Thus the majority concluded parliamentary authority in the form of an act of parliament is required for ministers to give notice because only parliament can disapply an act of parliament. '[W]e consider that, by the 1972 Act, Parliament endorsed and gave effect to the United Kingdom's membership of what is now the European Union under the EU Treaties in a way which is inconsistent with the future exercise by ministers of any prerogative power to withdraw from such Treaties' at .
The other ground in the appeal was whether legislative consent to withdrawal was required from the devolved assemblies of Scotland, Wales, and Northern Ireland. First, the majority in the Supreme Court held that while the devolution legislation required the devolved assemblies to observe and implement EU law, that legislation did not go further and require the UK to remain a member of the EU. Also, relations with the EU, like other matters of foreign affairs, are reserved to the UK parliament. 'Accordingly, the devolved legislatures do not have a parallel legislative competence in relation to withdrawal from the European Union' at .
Second, the Sewel convention that the Westminster parliament will not normally legislate on devolved matters without the consent of the devolved legislatures was a constitutional convention and not a law. Conventions are defined as non-legal but authoritative rules of political practice governing the exercise of power within the constitution. Conventions are unenforceable by the courts, but politically enforceable because of the adverse constitutional consequences that follow if they are not observed.
The Sewel convention was embodied in a memorandum of understanding between the UK government and the devolved governments in December 2001. The Scotland Act 2016 recognises the Sewel convention, but the convention remains a convention and has not become a law that requires the devolved legislatures to consent to the UK withdrawal from the EU. The majority in the Supreme concluded: 'The Lord Advocate and the Counsel General for Wales were correct to acknowledge that the Scottish parliament and the Welsh Assembly did not have a legal veto on the United Kingdom's withdrawal from the European Union. Nor in our view has the Northern Ireland Assembly'.
Constitution in action
Miller represents the culmination of a seven month battle as to where power lies in the constitution. This case shows the constitution in action in which the decision of Supreme Court confirms that there continues to be a separation of powers, with an independent judiciary not afraid to apply constitutional law against a powerful executive. The government is subject to the rule of law, or as Lord Denning said, 'be ye ever so mighty the law is above you'.
Triggering article 50 has to be authorised by parliament. But it must be said that while this is a legal defeat for the government the mood among ministers remains good because (i) they don't have to get formal consent from the devolved assemblies, and (ii) the Supreme Court did not set out the detail of the legislative authorisation of withdrawal but rather set out the minimum requirement that the UK parliament must authorise withdrawal.
The detail is a matter for parliament to agree on and the government has published a bill which contains just two clauses and is only 137 words long.
Clause 1 states: 'Power to notify withdrawal from the EU (1) The prime minister may notify, under Article 50(2) of the Treaty on European Union, the United Kingdom's intention to withdraw from the EU. (2) This section has effect despite any provision made by or under the European Communities Act 1972 or any other enactment.'
The aim is to keep the bill simple to avoid too many amendments. Although the government has provided only five days debate, the bill is likely to pass the House of Commons as Labour has agreed to support it. One conservative MP, Ken Clarke, will vote against the bill as will the fifty-nine Scottish National Party MPs, and nine liberal democrats MPs. Sixty Labour MPs are threatening to ignore the Jeremy Corbyn's three line whip to vote for the bill.
Despite this the government should have a majority to pass the bill. Ministers have warned that there will be a constitutional crisis if the House of Lords delays or rejects the bill so that notice of withdrawal cannot be given at the end of March. The prime minister has agreed to issue a white paper on the UK's strategy for leaving the EU although this likely to a repetition of her recent speech on that issue. Notice will eventually be given and that is when the real political slog with the EU begins, with many legal issues yet to be decided.
Simon Parsons is a qualified solicitor (non-practicing). He was an associate professor of law at Southampton Solent University