The High Court has today issued its Judgment in the dispute about the UK Parliament's necessary approval of a Brexit notification--see R (Miller) -V- Secretary of State for Exiting the European Union  EWHC 2768 (Admin). It has ruled that such Parliamentary approval is indeed required as a matter of UK constitutional and public law. The Government has already announced that it will appeal this decision to the UK Supreme Court (UKSC). The implications of such an appeal are important and need to be carefully considered. One such possible consequence is that the appeal (indirectly) brings the case to the docket of the Court of Justice of the European Union (CJEU).
In my view, an appeal of the High Court's Judgment before the UKSC will indeed trigger a legal requirement under EU law for the UKSC to send a reference for a preliminary ruling to the CJEU. I have rehearsed most of my arguments on twitter earlier (see here and here) and this posts brings them together.
Basic EU Law Background
Article 267(1)(a) TFEU establishes the monopoly of interpretation of the CJEU and it indicates the Court shall have jurisdiction to give preliminary rulings concerning the interpretation of the Treaties. Article 267(2) then goes on to enable the domestic courts of the Member States to issue request preliminary rulings from the ECJ where questions of interpretation of EU law are raised before them and they consider that a decision on the question is necessary to enable them to give judgment. However, that discretion of domestic courts to request preliminary rulings from the CJEU does not apply to the courts or tribunals of a Member State against whose decisions there is no judicial remedy under national law. In that case, Article 267(3) indicates that where a question on the interpretation of EU law is raised, the highest court shall bring the matter before the CJEU.
The uncertainties surrounding the interpretation of Art 50 TEU before the High Court
One of the extremely complex issues concerning the UK's potential withdrawal from the EU following the Brexit vote of 23 June 2016 concerns the interpretation of Article 50 TEU (on this, see here). One of the difficult sub-questions concerns the (ir)reversibility of an Art 50 TEU trigger notification. This is an essential element for an assessment of the UK's constitutional requirements for the delivery of such notification, as the High Court's Judgment makes clear.
Indeed, as a preliminary issue, in today's Judgment, the High Court has addressed the problematic interpretation of Art 50 TEU. Unanimously, the High Court has indicated that "Important matters in respect of Article 50 were common ground between the parties: (1) a notice under Article 50(2) cannot be withdrawn once it is given ..." para ; and that "Once a notice is given, it will inevitably result in the complete withdrawal of the United Kingdom from membership of the European Union and from the relevant Treaties at the end of the two year period, subject only to agreement on an extension of time ..." para .
There are two ways of interpreting the High Court's dealing with the argument on irreversibility of an Art 50 notification. First, that the High Court takes this approach in para  because it is common ground between the parties ex para --what I would call the UK procedural approach. Second, that the High Court has of its own interpreted an Art 50 notification to be irreversible ex para , which happens to align with the common position of the parties in para --what I would call the EU substantive interpretation approach.
The UK procedural approach is saved by the High Court's discretion under Art 267(2) TFEU to consider that the interpretation of Art 50 TEU is actually not necessary for it to adjudicate the matter at hand because this is not part of the controversy between the parties. However, the EU substantive interpretation does trigger some issues because, having recognised the interpretation of Art 50 TEU as an important aspect for the adjudication of the case, the High Court should not have taken it upon itself to interpret it and should rather have requested a preliminary ruling from the CJEU. However, unless under a very expansive interpretation of the principle of sincere or loyal cooperation in Art 4(3) TEU, this does not amount to a breach of EU law.
The uncertainties surrounding the interpretation of Art 50 TEU before the UK Supreme Court
Now, in case of an appeal of the High Court's decision before the UKSC, in my opinion, the referral to the CJEU is legally unavoidable (I will not deal for now with arguments of judicial politics or pragmatic views on the UKSC's likely course of action). Even if the parties do not challenge or even raise to the UKSC's consideration the matter of the (ir)reversibility of and Article 50 notification, it is a logical given that the UKSC needs to take a stance (even if implicit) on this point in order to be able to rule on the case. If it quashes the High Court's decision, it needs to clarify the points of law which the High Court would have gotten wrong--one of which concerns the irrevocability of an Art 50 notification. if it upholds the High Court's decision, it is (implicitly) accepting the assumption that an Art 50 notification is irrevocable. Either way, the UKSC cannot escape a substantial (implicit) consideration of the interpretation of Article 50.
In my view, this engages the UKSC's obligation to request a preliminary ruling from the CJEU under Article 267(3) TFEU and not doing so triggers a risk of infringement of EU law by the UK due to the acts (or omission, in this case) of its highest court.
Semi-Advanced EU Law Background
The UKSC's obligation to request a preliminary reference from the CJEU is controlled by the so-called CILFIT test, which establishes that "a court or tribunal against whose decisions there is no judicial remedy under national law is required, where a question of [EU] law is raised before it, to comply with its obligation to bring the matter before the Court of Justice, unless it has established that the question raised is irrelevant or that the [EU] provision in question has already been interpreted by the Court or that the correct application of [EU] law is so obvious as to leave no scope for any reasonable doubt. The existence of such a possibility must be assessed in the light of the specific characteristics of [EU] law, the particular difficulties to which its interpretation gives rise and the risk of divergences in judicial decisions within the [EU]" (283/81, EU:C:1982:335, para 21).
What does this mean for the UKSC in the Brexit litigation in case of appeal?
In short, my understanding of the CILFIT test is that a highest court of a Member State (the UKSC) must request a preliminary ruling on the interpretation of the Treaties to the CJEU and has no discretion not to do so unless: (a) the question is (objectively) irrelevant for the adjudication of the case, or (b) the provision has already been interpreted by the CJEU, or (c) there is no scope for reasonable doubt in the interpretation of the provision. None of these apply in the specific case of the Article 50 litigation.
First, it is inconceivable to me to argue that the interpretation of Art 50 and the (ir)revocability of a notice under it is irrelevant for the adjudication of this case. A different issue would be whether the UKSC could pragmatically sidestep the need to engage in that interpretation, either by presuming its content (the EU substantive interpretation approach mentioned above), or by insisting on the fact that it is common ground to the parties to the litigation and, therefore, the issue of the (ir)revocability of the notification is not (formally, explicitly) raised before it (the UK procedural approach.
However, in my opinion, neither of these avoidance strategies would meet the basic requirements of good faith in the interpretation of the CILFIT test, coupled with Article 4(3) TEU, which requires the domestic court to assess the need to request a preliminary ruling "in the light of the specific characteristics of [EU] law, the particular difficulties to which its interpretation gives rise and the risk of divergences in judicial decisions within the [EU]". The interpretation of Article 50 TEU is, to put it simply, the most relevant EU constitutional law issue since the OMT litigation and one of the top, if not the top, EU constitutional law issue since the entry into force of the Lisbon Treaty. Engaging in semantics in the analysis of the first prong of the CILFIT test against this background (ie, stretching the narrow interpretation "irrelevant") seems to me logically and legally unacceptable.
Second, it is plain that Art 50 has not been interpret by the CJEU yet. And, thirdly, it is also plain that there is scope (massive scope, a gaping hole) for reasonable doubt in the interpretation of Article 50 TEU. Thus, the so-called acte claire doctrine (ie the counterbalance of the CILFIT test) simply does not apply here.
Overall, in my opinion, the UKSC has an absolute and inexcusable obligation to request a preliminary ruling on the interpretation of Article 50 TEU from the CJEU the moment the appeal against the High Court's Judgment (eventually) reaches its docket. Otherwise, the UKSC risks triggering an infringement of EU law and eventually creating liability in damages under the Kobler / Traghetti del Mediterraneo strand of case law on State liability. Again, I am not dealing with the arguments on the likelihood of an actual infringement case brought forward by the European Commission, or the CJEU's eventual decision. I am, for now, simply stressing the state of EU law, which the UKSC would be well advised to bear in mind and uphold, unless it aims to contribute to the deterioration of the rule of law in the UK and the EU (which is something that keeps me awake at night).