The Divisional Court has today (3 November 2016) determined that the decision to issue the Article 50 notice that will trigger Brexit must be made by Parliament and not the government – R (Miller) v Secretary of State for Exiting the EU.
Before saying anything else, there are three initial observations that should be made about this.
The first is that it is just the outcome of a preliminary skirmish. The decisive legal battle will be fought in the Supreme Court next month. The government has already announced its intention to appeal the case, and there is no question that it will get permission to do so. In spite of the significant media interest in today’s judgment, nothing has been finally determined.
The second thing is that the judgment is, nonetheless, hugely important. The Divisional Court was as strongly constituted as it could have been – the Lord Chief Justice, Master of the Rolls, and Lord Justice Sales. In a lucid and robust decision, the judges were unanimous and expressed no reservations about their conclusion or the reasoning that led them to it. Their judgment effectively changes the terms of the debate about when and how Brexit will happen. It determines the context in which the Supreme Court case will be heard.
The third point is that the judgment should come as no surprise. A number of lawyers who were willing to express a clear opinion (myself included) thought that the claimants in Miller had much the better of the legal argument, for the reasons I set out in an earlier post ‘Why the UK Parliament Still Needs to Vote for (or against) Brexit‘. Naturally this was not a unanimous view, and the Supreme Court could yet go the other way. But the arguments against the government are very powerful, as the judgment in Miller fully demonstrates.
Subject to these observations, what did the Court decide, and what does it mean?
There are many legal complexities in the case, but in some ways it is also quite simple. The essential elements of the judgment can be summed up in the following propositions [with paragraph references for those who want to read more].
1. The Referendum
Parliament made no provision in the EU Referendum Act 2015 for the referendum vote to have any legal effect . It was therefore only ‘advisory‘ in nature . The outcome of the referendum was solely a ‘political event‘ .
Consequently, nothing in the Referendum Act provides any legal basis for the government to issue an Article 50 notice.
2. The Prerogative
Since it has no statutory authority, the government had to reach for the ‘royal prerogative’ as the source of its power to trigger Brexit.
The prerogative is what is left of the once very extensive powers which, in medieval times, vested in the Crown. One area in which it continues to operate is the field of international law – it remains the source of the power which is used to make, and unmake, international treaties between the UK and other nation states .
Since the UK’s relationship to the 27 other member states of the EU is defined by a series of treaties – Article 50 being a provision of one of them (the Treaty on European Union) – the government claimed that it could use the prerogative to trigger an exit from the EU.
The problem with this is that the reason why the prerogative powers are now just a residue of what they once were is that they have been systematically eroded over many years. In fact one of the most important aspects of UK constitutional history is how the powers of the Crown came to be limited at the expense of those of Parliament. In this constitutional struggle, most of the major battles (both literal and metaphorical) were fought during the 17th Century. They culminated in the decisive Parliamentary victory reflected in the 1689 Bill of Rights .
Since then, Parliamentary sovereignty has been the dominating constitutional principle in the UK . And a key feature of Parliamentary sovereignty is that ‘primary legislation is not subject to displacement by the Crown through the exercise of its prerogative powers’ .
The prerogative is only available for a case that is not already covered by statute .
3. The European Communities Act 1972
The problem for the government then is that the UK’s membership of the EU is covered by statute – the European Communities Act 1972 (ECA).
There are particular reasons why this had to be the case. Most international treaties only have legal effect ‘on the plane of international law‘  – that is, they do not change the domestic law of the countries which enter into them. However, EU membership is unique, and could never have worked on this restricted basis. Under the EU Treaties, EU law has to have effect as part of the domestic law of member states.
In order to achieve this outcome, Parliament had to legislate in the form of the ECA – ‘only Parliament could create the necessary changes in national law to allow EU law to have effect at the level of domestic law which the Treaties required‘ .
Having done this, the ECA became part of the constitution of the UK, with ‘such importance in our legal system that it is not subject to the usual wide principle of implied repeal by subsequent legislation‘ .
4. The Effect of Article 50
The ECA therefore is a constitutional statute, the consequence of which is to generate a series of rights for UK citizens which will be lost on Brexit [57-61].
It is no answer to this loss of rights for the government to say that some of them may (and in any event, not all of them can) be replaced by legislation enacted after Brexit . The fact is that once an Article 50 notice is served on the European Council ‘it will inevitably result in the complete withdrawal of the United Kingdom from membership of the European Union…The effect of the giving of notice under Article 50 on relevant rights is direct, even though the Article 50 process will take a while to be worked through‘ .
In other words, if the Article 50 notice was issued by the government, the consequence is that ‘the Crown, through exercise of its prerogative powers, would have deprived domestic law rights created by the ECA 1972 of effect‘ .
5. The Prerogative v Parliament
All of this gives rise to the core argument on which the outcome of the case depended.
The key question was as follows. Since it is well-established that the prerogative cannot be used to displace primary legislation, and since the inevitable effect of giving an Article 50 notice will be to fatally undermine a piece of primary legislation (the ECA), how could the government consider that it could still rely on the prerogative power?
The government’s argument was that under the ECA Parliament legislated to give effect to the EU Treaties for so long as they were in effect, but left to the government the question of whether or not they would be . The government was free to employ the prerogative power at any time, and only if Parliament had expressly legislated to remove that power would the government have lost its right to use it.
The most important part of the judgment is its forceful response to this legal argument. At its heart, the decision of the court is summed up by the following statement –
‘The wide and profound extent of the legal changes in domestic law created by the ECA 1972 makes it especially unlikely that Parliament intended to leave their continued existence in the hands of the Crown through the exercise of its prerogative powers. Parliament having taken the major step of switching on the direct effect of EU law in the national legal systems by passing the ECA 1972 as primary legislation, it it not plausible to suppose that it intended that the Crown should be able by its own unilateral action under its prerogative powers to switch it off again.‘ 
In other words, the reality is that Parliament had stepped into the fray and displaced the prerogative by the mere fact of legislating. It is unrealistic (‘not plausible‘) to suppose that it always intended that this legislation could be rendered a dead letter by the government at any time. Since the ECA is a constitutional statute, it cannot be impliedly repealed even by Parliament itself; it is even less likely that Parliament meant to allow the government to achieve its de facto repeal by executive action .
On the contrary, the reason why the prerogative can be used in the sphere of international relations is precisely because that generally has no effect on domestic law. In the unusual situations where, as in the case of EU membership, there would in fact be such an effect, the government should have realised that the prerogative was not available to it .
A detailed analysis by the court of the provisions of the ECA  and of previous case law on the limits of the prerogative [97-101] supported these conclusions.
Indeed, so far from Parliament needing to have expressly stated that the prerogative was disapplied, the position was, as the claimants argued, the precise opposite. Only if the ECA had either expressly or by necessary implication preserved the prerogative powers of the Crown to issue an Article 50 notice would the government have been able to trigger Brexit without further legislation to empower it to do so .
Meaning and Effect
The simplicity of the case lies therefore in the fact that it comes down to a fundamental constitutional clash between Parliament and the Crown. Once Parliament had occupied the relevant legal territory by passing the ECA, there was no room for the residual powers of the Crown, which had been displaced and were no longer available.
Students of constitutional history should scarcely raise an eyebrow. As long ago as 1610, the constitutional jurist, Sir Edward Coke, declared in the Case of Proclamations that ‘the King hath no prerogative but that which the law of the land allows him‘ . Miller is merely an example of an English court, in November 2016, saying essentially the same thing.
What next – Hard or Soft Brexit?
However, this is not the last word. The case will now leapfrog to the Supreme Court, where four days from 5 to 8 December have been reserved to hear it.
If the Supreme Court adopts the same approach as the Divisional Court, the implications will be significant, although not necessarily in the way that the claimants in Miller might originally have hoped.
At the outset of the case, there was a barely disguised intention by at least some of the claimants to put a spoke in the wheels of Brexit. The need for a Parliamentary vote, it was suggested in some quarters, would provide an opportunity to override the outcome of the referendum, or at least give rise to a re-run.
The mood music has changed a lot since then. Whatever Theresa May’s personal views on the EU, she has the imperative of holding her party together. If ‘Brexit means Brexit‘ it is for the overriding reason that, if it means anything else, the Tory Party will split irreparably.
In fact, widely derided as it has been, May’s tautological formulation has done a great deal to shape the political debate and generate a sense of inevitability about the UK’s exit from the EU. Perhaps the outcome of Miller will change this narrative. More likely, however, its effects will be felt not in determining whether or not the UK leaves the EU, but in shaping when that happens and precisely what type of Brexit we get.
It is a rare court judgment which causes fluctuations on the currency market. The value of sterling rose when the judgment in Miller was released because the market anticipated that this made a ‘Hard Brexit’ – at its simplest, a sacrifice of access to the single market in order to gain control over immigration – much less likely.
In all probability, this is correct. If Parliament must legislate to sanction the issue of an Article 50 notice, it also obtains control over the basis on which that notice may be given.
Not only is this likely to push the timing of the notice back beyond the March 2017 date previously suggested by the Prime Minister – raising the (perhaps sensible) prospect that it will not be done until after the French and German elections – but it provides significant opportunity through Parliamentary debates and amendments for the legislature to dictate a UK negotiating stance that involves softer forms of Brexit than the government appears to have been contemplating.
It raises, in other words, the prospect of a frank debate about the form the UK wants Brexit to take; not taking place in the sealed environment of a Cabinet meeting, but in the open forum of Parliament. This will be very welcome news for the media, a gift for lobbyists and industry groups, a nightmare for the party whips, and an encouragement for all those who want a Soft Brexit entailing the retention of access to the single market.
As it happens, many of the MPs who have appeared to lean in favour of a Hard Brexit are those who also argued most strongly during the referendum campaign for the principle of Parliamentary sovereignty.
Unless the Supreme Court on appeal takes a radically different view of the arguments in Miller – which, at least in my view, it should not – Parliamentary sovereignty is precisely what the case will have upheld. Perhaps ironically, that also means that this is likely to have been a bad day for the supporters of a Hard Brexit.