Today the Supreme Court has published its widely anticipated Judgment on whether the UK Government is required to obtain the approval of Parliament to give notice under Article 50 TEU to trigger Brexit negotiations.

We summarise the reasons for the decision and consider whether it will, in fact, have any real impact on the timing and scope of negotiations over the UK's departure from the EU.

The issue for the Supreme Court

The narrow issue determined by the Supreme Court was whether formal notice of the UK's withdrawal from the EU could be given by ministers, without the need for prior legislation passed in the UK's Houses of Parliament.

The Supreme Court affirmed the decision of the lower Court, finding that ministers could not use their prerogative powers to give notice under Article 50. As a result, the government will need to table what it says will be a 'short' piece of legislation for parliamentary approval before the UK can give notice.

The Supreme Court's main findings

The central plank of the government's argument was that as a matter of constitutional law, ministers may legitimately use their prerogative powers to freely enter into and to terminate international treaties without recourse to Parliament. By extension the government argued that this principle also applied to treaties governing the UK membership of the European Union.

The Supreme Court rejected this analysis, relying on a number of established principles of constitutional law:

Firstly, the prerogative power to make treaties is exercised on the basis that those treaties have effect only in an international law context. The treaties do not take effect, in themselves, as part of UK law and do not give rise to any legal rights or obligations in UK domestic law.

Secondly, since the 17th century it has been a '…fundamental principle of the UK constitution that unless primary legislation permits it, the Royal Prerogative does not enable ministers to change English common or statute law.'

Applying these two principles to the TEU (as implemented through the European Communities Act 1972), the Supreme Court observed the following.

The 1972 Act was 'unprecedented'. Not only did it prescribe the content of domestic law in areas covered by the TEU, but it '…authorises a dynamic process by which, without further primary legislation (and in some cases even without any domestic legislation) EU law not only becomes a source of UK law, but actually takes precedence over all domestic sources of UK law, including statutes.'

The 1972 Act is, exceptionally, a 'conduit pipe' by which EU law is introduced into UK domestic law. EU law is, therefore, a direct source of UK domestic law. It follows that ministers cannot use prerogative powers to turn off that source, without the approval of Parliament.

Devolved legislatures – Scotland, Northern Ireland and Wales

The Supreme Court held that the UK's decision to withdraw from the EU was a matter reserved to the UK government. Devolved administrations in Scotland, Northern Ireland and Wales did not have a veto on the UK's decision to withdraw from the EU. This will no doubt be a source of immense frustration to voters in Scotland, where the majority voted to remain within the EU.

Comments upon the effect of leaving the EU on UK domestic law

In reaching its conclusions, the Supreme Court made a number of comments about the impact of leaving the EU on the UK's domestic law; stating:

" EU law will cease to be a source of domestic law for the future (even if the Great Repeal Bill provides that some legal rules derived from it should remain in force or continue to apply to accrued rights and liabilities), decisions of the Court of Justice will (again depending on the precise terms of the Great Repeal Bill) be of no more than persuasive authority, and there will be no further references to that court from UK courts. Even those legal rules derived from EU law and transposed into UK law by domestic legislation will have a different status. They will no longer be paramount, but will be open to domestic repeal or amendment in ways that may be inconsistent with EU law."

While these changes are potentially significant, it remains to be seen whether the government will have the inclination (or the time) in the short term to embark on a wholesale rewriting of domestic law. In the interests of stability, it is more likely that any 'Great Repeal Bill' will leave many 'EU-based' statutes and regulations intact, at least for the time being.

Impact on the timetable for Brexit

The Supreme Court's analysis included a fairly blunt critique of the statute implementing the referendum, which did not set out the procedure to be followed in the event of a vote to leave the EU. The subtext appears to be that the constitutional problem caused by the proposed use of prerogative powers (and any delay in the Brexit timetable as a result of the Court's intervention) is of the government's own making.

Notably, in its Judgment, the Supreme Court referred to the following paragraph from a 2009-10 Select Committee Report on the Constitution:

“Because of the sovereignty of Parliament, referendums cannot be legally binding in the UK, and are therefore advisory. However, it would be difficult for Parliament to ignore a decisive expression of public opinion.”

It would seem very unlikely, therefore, that Parliament would vote against triggering the UK's withdrawal from the EU.

That said, the Scottish Nationalist Party and the Liberal Democrats have already indicated that they intend to vote against the legislation necessary to trigger notice under Article 50. The SNP also intends to slow the progress of the legislation through Parliament by proposing 'over fifty' amendments to the current draft bill.

The UK government, meanwhile, has confirmed that it will abide by the Supreme Court's decision. It maintains that having to obtain parliamentary approval will not impact on its intention to trigger Brexit negotiations in March. Looking at the current make up of Parliament, the Conservatives have a working majority which is likely to mean that the legislation required as a result of the Supreme Court Judgment should be passed through the House of Commons without difficulty, even with the SNP and Liberal Democrats (and potentially some Labour MPs) in opposition.

The House of Lords is perhaps a more difficult proposition, as the government does not have a working majority. Some commentators report 'murmurings of an organised attempt to resist Article 50' in the Lords, although most agree that the legislation necessary to trigger Article 50 will, ultimately, be passed.

While the Miller & Santos decision serves as an important analysis of the relationship between the UK government and parliament (which is all the more significant given that the UK does not have a codified constitution), it is far from clear whether the outcome of the case will have a material impact on the progress and nature of the UK's exit from the EU.