Broadly restating the ancient principle that Parliament holds dominant power in Britain’s national government, even while vigorously exercising its own authority to declare what laws mean, the United Kingdom Supreme Court ruled in a divided decision on Tuesday that only Parliament can take the step of pulling out of the European Union.
The 8-to-3 decision – the first ever made with all 11 members of the court taking part — was a stern reminder of how far royal authority and the power of the monarch’s ministers has further diminished in modern times. The Queen’s government does retain powers over diplomacy and war, but the range of its domestic powers reduces it to what the court majority termed that of “the junior partner,” constitutionally speaking.
“We cannot accept that a major change in UK constitutional arrangements can be achieved by ministers alone; it must be effected in the only way that the UK constitution recognizes, namely by Parliamentary legislation,” the majority wrote in rejecting the government’s basic claim that the Prime Minister – using the Queen’s “royal prerogative” –could take the initial step in the so-called “Brexit” process of leaving the 28-nation European Union.
The decision did not specify the type or range or new legislation that Parliament would have to take to initiate the two-year process of declaring British independence from her sister nations on the Continent. Many British laws will have to be changed or altered to ultimately carry out the break, but the court suggested that the initial step of formally invoking “Brexit” could be done by a very simple piece of legislation.
Even so, the court instructed that the action must come in the form of “primary legislation” – the type of measure that has the full authority of Parliament behind it. In fact, the opinion declared that a mere motion in the House of Commons (the “lower” house of Parliament) urging the Prime Minister to start “Brexit” would not be sufficient. The majority dismissed as of no effect legally just such a motion, passed by the House early last month as an expression of support for the plan of Prime Minister Theresa May to begin the process by the end of March.
The Prime Minister, who is scheduled to pay an official visit to the U.S. and President Trump on Friday, has made it clear in a recent speech that she plans to try to work out a complete separation of Britain from all of the EU institutions, including the role that the European Court of Justice has had to override the meaning of EU law as it applied in Britain and the other member countries.
The actual terms of leaving the EU will have to be negotiated over a period of two years, as specified by the EU treaty under which Britain joined as a partner in the common enterprise of European governance.
While the new ruling relied heavily upon constitutional principles in favor of Parliament’s ultimate sovereignty going back to the early 1600s, the legal key to Tuesday’s decision was the interpretation that the court’s majority made of the 1972 act by Parliament that authorized Britain to enter the EU in the first place. Nothing in that act, the majority ruled, in any way gave the Queen’s government the authority – on its own – to invoke the section of the EU treaty that permits a nation to withdraw.
Noting in detail just how much of its national governing independence that Britain gave up with Parliament’s permission 45 years ago, the court majority said that the nation’s constitution would not tolerate the reclaiming of that independence by the sole action of the Queen’s ministers.
In essence, the court majority indicated, Britain handed over to multi-national EU institutions the authority to dictate much of what could be done, or not, under Britain’s own domestic law. An action that profound, it said, could only be undone by Parliament itself.
Under Brexit, many laws in Britain – and, in particular, laws that deal with the rights of Britons in other EU countries and with the rights in Britain of other EU countries’ citizens – will simply be nullified when separation ultimately becomes a reality. The loss of those rights, the majority concluded, gave to two British individuals who would lose some of those rights the legal opportunity to sue to make sure that Brexit only occurred with Parliament’s formal blessing.
The former government of Prime Minister David Cameron had gained authority from Parliament in 2015 to hold a national referendum on whether British should leave or stay in the European Union. That vote was held in June, and exit (now popularly known as “Brexit”) was approved by a narrow margin. The result led to the fall of the Cameron government, now succeeded by the May ministry.
The British court conceded that the June vote has had major political consequences, but it said that the fact that a majority had voted for Brexit had no bearing on the legal question of how the exit process could be started as a formal, official act.
The majority of eight Justices spoke through a single 47-page opinion signed by each of those members of the court, including its president, Lord Neuberger, and its vice president, Lady Hale. The three dissenting judges – Lords Reed, Carnwath and Hughes – each wrote a separate opinion. The dissents were in disagreement with the conclusion that only Parliament could trigger the Brexit process.
While the court was divided on that main point, it was unanimous in another facet of the decision – a conclusion that the move to trigger Brexit could be made without seeking the consent of the separate legislatures in Scotland, Wales and Northern Ireland (with England, the other parts of the UK). In modern times, those regional legislatures (now referred to as “devolved” legislative bodies) have been granted increased powers of home rule, including promises that their consent would be sought – at least some of the time – when the Parliament in London took action affecting those regional areas of the UK.
With Tuesday’s ruling, the May government is expected now to move quickly to draft legislation to carry out the mandate that it be Parliament’s formal choice to start the process.

(This post also appears today at Constitution Daily, the blog of the National Constitution Center in Philadelphia.)