Brexit in the Supreme Court: the arguments

On 5 December, the UK’s highest court will hear legal arguments on whether the government can launch Brexit without an Act of Parliament. What are the parties likely to tell the judges?

The government’s case relies on its inherent powers to make and unmake treaties

The government argues that ministers have always used their prerogative powers, also described as inherent or executive powers, to sign treaties with other countries. But international treaties, by themselves, do not change the laws of the United Kingdom. So legislation is needed to put them into effect.

None of that is disputed by the other side. But the government goes on to argue that it can continue to use prerogative powers to make or unmake treaties even if parliament has previously given effect to those treaties through legislation. “That fact,” it says, “carries no implicit restriction on how the government should or must later act in relation to those treaties on the international plane.” The powers have never been taken away by parliament.

The government signed a treaty in January 1972 allowing the UK to join what is now the EU. That was followed later in the year by an Act of Parliament called the European Communities Act 1972. It’s this law that gives people in the UK rights and duties under whatever EU treaties happen to be in force at any particular time. And the government can change those rights and duties through treaty negotiations with the EU, which are conducted under prerogative powers.

So, says the government, it can use those powers to create or remove rights and obligations for people in the UK. New legislation is not required to trigger Brexit and the High Court was wrong to say it was.

The first respondents argue that EU treaties are a special case

Lord Pannick QC, counsel for first respondent Gina Miller, says the government’s argument fails to recognise the exceptional constitutional nature of the European Communities Act 1972.

When parliament has incorporated international rights into domestic law, “prerogative powers cannot lawfully be used on the international plane to destroy the rights recognised by parliament as part of domestic law”.

Parliament never intended to give a minister the power to defeat or frustrate the rights it created in the 1972 Act, Lord Pannick argues. If it had meant to do that it would have said so. The Brexit Secretary had failed to show there was “clear statutory power authorising him to defeat statutory rights”.

Only parliament can take away the rights that parliament created in the 1972 Act, adds Lord Pannick. These include access to the EU Court of Justice and rights such as free movement in Europe.

Where parliament has created statutory rights—and, in particular, rights of constitutional significance—the minister has no prerogative power to take action which will defeat those rights. “Clear statutory authority is needed,” Lord Pannick concludes. “There is no such authority.”

Lawyers for the second respondent stress parliamentary sovereignty

For Deir Dos Santos, Dominic Chambers QC argues that what the government is proposing to do undermines parliamentary sovereignty and the Bill of Rights 1688. “Once treaty obligations are committed to domestic law, these laws cannot be removed by simply withdrawing from the treaty.”

Quoting from the High Court judgment, Mr Chambers says the Brexit Secretary’s argument on prerogative powers is flawed at a basic level. “His mistake is to treat the royal prerogative of making and unmaking treaties as if it were an independent, and monolithic, source of domestic power and authority unconditioned by other constitutional principles—vitally, in this case, the doctrine of the parliamentary sovereignty,” says Mr Chambers.

“From that erroneous starting point, [the government] asserts the constitutionally misconceived proposition that the executive exercising the treaty making and unmaking prerogative can override or nullify primary legislation (or the common law). That is, with respect, a proposition which only has to be stated to be rejected.”

Both sides mention the referendum

The government says it’s a “surprising” consequence of the High Court judgment that, for the UK to leave the EU, “Parliament must be asked to answer precisely the same question which was put by Parliament to the electorate and has been answered in the referendum; and must give the same answer in legislative form”.

It was the clear understanding of all concerned that that government could use its existing prerogative powers to give effect to the “leave” vote, the Brexit Secretary says. A leaflet sent to every household in the UK said: “This is your decision. The government will implement what you decide.”

The European Union Referendum Act 2015 said nothing about the consequences of a “leave” vote, according to the government, because there was no need to. That Act left the scope of the prerogative powers unaffected.

But if that’s true, says Dominic Chambers, then the UK could have withdrawn from the EU at any time—without a referendum, without scrutiny from parliament and without anything else. “That is a startling result,” he adds, “and it cannot be right.” He points out that Parliament chose not to say that the Brexit referendum would be legally binding—unlike, for example, the alternative vote referendum in 2001.

And Lord Pannick says the High Court was right to conclude that government promises are not binding on the courts. As the Victorian constitutional writer Professor AV Dicey wrote, “the judges know nothing about the will of the people except in so far as that will is expressed by an Act of Parliament”.

Expect to hear about the unique position of Scotland…

The Lord Advocate, Scotland’s senior law officer, has been given permission by the Supreme Court to intervene in the case on behalf of the Scottish government.

He agrees with the respondents that notification under Article 50 of the Treaty on European Union would require an Act of the UK parliament. But, says the Lord Advocate, any bill brought before the UK parliament for that purpose would face an additional hurdle.

Article 50 permits a state to withdraw from the EU “in accordance with its own constitutional requirements”. Under the UK’s uncodified constitution, the Lord Advocate says, these requirements include conventions as well as law. Conventions are rules of behaviour that are accepted as binding by all concerned.

One such convention, the Sewel convention, is acknowledged in the Scotland Act 1998. The Act says that “it is recognised that the parliament of the United Kingdom will not normally legislate with regard to devolved matters without the consent of the Scottish Parliament”.

When needed, that consent is obtained by asking the Scottish Parliament to pass what’s called a legislative consent motion.

The Lord Advocate argues that a bill authorising the UK to give notice under Article 50 would change the lawmaking powers of the Scottish parliament and therefore a legislative consent motion would be needed.

Using the prerogative to trigger Article 50 would, the Lord Advocate concludes, “circumvent the requirement for the UK and Scottish parliaments to address whether, under established constitutional convention, the consent of the Scottish Parliament should be sought for such changes”.

…and Wales…

Mick Antoniw, Counsel General for Wales, has been given permission to intervene on behalf of the Welsh government. He agrees that prerogative powers cannot be used to affect statutes with constitutional status. He also argues that triggering Brexit would engage the Sewel convention.

This applies to Wales and Northern Ireland as it does to Scotland. It is not yet included in legislation covering Wales, but the Wales Bill, currently before the UK parliament, would add it to the Wales Act 2006 in similar terms to the Scotland Act.

Like the Lord Advocate, the Counsel General is not arguing that a devolved assembly has a veto on legislation passed by the UK parliament. “He is therefore not asking the court to enforce the convention,” his counsel says. “Rather, he submits that there can be no prerogative power to short-circuit the Sewel convention which in giving proper respect to, and grounding a process of dialogue with, the devolved legislatures is a fundamental part of the United Kingdom’s devolution framework.”

..and Northern Ireland

John Larkin QC, Attorney General for Northern Ireland, broadly supports the UK government’s position. “On the day after notice is given under Article 50”, he says, “the law of the United Kingdom will be the same as it was on the day before notice was given.” The prerogative would not be used to repeal or undermine legislation—such as the Act that allows elections to the European Parliament. That Act would still be law, although “no longer a particularly useful part of the statute book”.

Mr Larkin then addresses devolution issues raised by the High Court of Northern Ireland. Such issues deal with the powers and functions of the executive and assembly in Northern Ireland.

The Attorney General argues that nothing in the relevant Northern Ireland law requires an Act of the UK parliament before the government can give notice under Article 50. Even if it did, the consent of the Northern Ireland Assembly would not be required.

Nor, he adds, do the relevant laws and agreements prevent the government from using its prerogative powers.

Other applicants, interveners and interested parties

The Northern Ireland government is involved because of a Brexit challenge by local campaigners and politicians that began in the Belfast High Court. Their arguments will also be heard next week.

In addition, two different groups of people concerned about their rights as EU citizens will address the court as interested parties. A further group of 'expat interveners', as well as the Independent Workers Union of Great Britain, have been given permission to intervene. Finally, the judges will see written submissions from a campaign group called Lawyers for Britain.