As a consequence of the European Union (withdrawal) (No. 2) Act 2019, the European Council (EC) is bound to consider granting the UK a further extension on the Article 50(3) negotiating period, if, by 19 October 2019, the UK parliament has neither approved the terms by which the UK leaves the European Union (EU) with a legal agreement and political declaration in place, nor approves a proposal to exit the EU without any such agreement. The obligation on the EC to consider an extension on Article 50(3) will arise irrespective of whether or not the UK Prime Minister formally makes an extension application. The result of an extension, if granted, is that the date for the UK’s exit from the EU will be reset for 31 January 2020.
Paragraphs 1 and 2 of Article 50 of the Lisbon Treaty, read in conjunction with the European Union (withdrawal) (No. 2) Act and the recent decision of the UK Supreme Court in the case of R (Miller) v The Prime Minister  UKSC 41, lend weight to the above propositions. Drawing on these sources, I will argue that if the circumstances arise in which an extension of Article 50(3) is considered by the EC, then, in order to comply with its obligations under Article 50, the EC will grant the UK an extension. However, it will condition the extension on the UK parliament’s approval of the Withdrawal Agreement and the Joint Statement supplementing the Political Declaration, which was agreed between the EC and the UK government on 25 November 2018. By its decision of 22 March 2019, when it agreed to the first extension request made by the UK government, the EC came close to the position I advocate (EC Decision 2019/476, para. 9). It is now time for the EC to restate its position without the qualification contained in that decision.
Article 50 of the Treaty of Lisbon places two clear obligations on the EC in the event that a member state determines to leave the EU. First, paragraph 1 of the Article requires that the EC respects the “constitutional requirements” of the departing member state - in so far as such “requirements” determine how that member state should withdraw from the EU. Second, paragraph 2 obliges the EC to “negotiate and conclude an agreement with that State…”. The obligations contained in paragraphs 1 and 2 of Article 50 are paramount. They must frame the EC’s approach to all stages of the Brexit negotiations, including when determining whether or not to grant an extension in accordance with Article 50(3).
As regards the first obligation, the fact that, on two occasions, the UK government has been found to have shown disregard for its own constitutional arrangements in the process of its leaving the EU (see: R (Miller) v Secretary of State for Exiting the European Union  UKSC 5 & R (Miller) v The Prime Minister  UKSC 41) does not lessen its force as far as the EC is concerned. Indeed, it is arguable that the UK government’s continuing default places an additional burden of vigilance on the part of the EC to ensure that the terms of paragraph 1 of Article 50 are fully respected.
Two UK Supreme Court decisions have identified the “constitutional requirements” which, per Article 50(1), the EC must have regard to in the context of the UK’s decision to leave the EU. UK “constitutional requirements” are contained within “two fundamental principles” (Miller , para. 41). These are the principles of parliamentary sovereignty and parliamentary accountability. In Miller [2017), the principles required an Act of Parliament to be passed before the UK government could trigger the Article 50 process by giving notice to the EC of its intention to leave the EU. In the most recent decision of the court, the principles were breached by the Prime Minister’s decision to prorogue parliament “from a date between 9th and 12 September until 14 October” (Miller , para. 1). The decision, which was “not a normal prorogation in the run-up to the Queen’s Speech” (Miller , para. 56), without “good reason” (Miller , p. 61) “prevented parliament from carrying out its constitutional role for five out of a possible eight weeks” (Miller , para. 56). Relevant to the Brexit process was the court’s finding that whilst “[s]uch an interruption in the process of responsible government might not matter in some circumstances...the circumstances ...were...quite exceptional. A fundamental change was due to take place in the Constitution of the United Kingdom on 31st October 2019” (Miller , paras. 57).
So, following the two UK Supreme Court decisions, especially the latter decision in Miller , the words "Member State concerned” in Article 50(3), when applied to the Brexit situation, must be construed as referring to the UK parliament. On this construction, the EU Treaties will cease to apply to the UK after the fixed period specified in Article 50(3), unless the EC, in agreement with the UK parliament, unanimously decides to extend the period. For we now know that the UK parliament alone controls the constitutional arrangements which will enable the UK’s exit from the EU in a manner that is consistent with Article 50. It is, therefore, doubtful whether a formal letter of request from the UK Prime Minister is necessary to trigger the EC’s obligation to consider an extension. By enacting the European Union (withdrawal) (No. 2) Act 2019, the UK parliament has made known its intention to seek an extension to Article 50(3) in the event that by 19 October 2019 there is neither a withdrawal agreement in place, nor an agreement to leave the EU without a withdrawal agreement. What can be said with more certainty is that the Prime Minister’s expressed reluctance to seek a further extension, and, more generally, his claim that the UK will leave the EU on 31st October 2019 in any event, must be disregarded by the EC - if the EC is to demonstrate that, as required of it by Article 50(1), it respects the constitutional requirements of a departing member state. The political and economic situation colloquially referred to as “no-deal Brexit” is clearly contrary to the will of parliament. As the court in Miller  put it “the House of Commons has already demonstrated, by its motions against leaving without an agreement and by the European Union (Withdrawal) (No 2) Act 2019, that it does not support the Prime Minister on the critical issue for this Government at this time …” (at para. 57).
The obligation on the EC to respect the constitutional requirements of a departing member state is an onerous one. It is a strict obligation. However, it is not an absolute obligation. The obligation falls short of requiring the EC to resolve two seemingly opposing intentions that the UK parliament might express in relation to the UK’s planned exit from the EU. In circumstances where the UK parliament expresses two or more seemingly contradictory intentions, it is open to the EC to seek ways to avoid the contradiction - provided that it does so within the general terms of Article 50.
This is the current situation in parliament. It is correct that the UK parliament has “demonstrated by its motions against leaving without an agreement” (Miller , para. 57) that its intent is to leave the EU with a deal. At the same time, after three separate motions, the UK parliament has rejected the only legal agreement and political declaration that has emerged through the Article 50 negotiating process. The obligation to bring about an agreement with a departing member state is the second of the core duties which Article 50 imposes on the EC, and there is nothing in the wording of the Article to suggest that it does not stand on an equal footing to the obligation to ensure that any exit from the EU occurs in accordance with the departing member state’s constitutional requirements. According to Article 50(2), the EC, on behalf of the EU, “..shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union”. In the context of the UK’s decision to leave the EU, the EC complied with this obligation on 25 November 2018.
There are many issues which have complicated the process of the UK leaving the EU - the vast majority of which have little to do with the terms of Article 50. However, when it comes to decisions made by the EC in the context of Brexit, Article 50 contains the only valid guiding principles. Thus, in the highly likely event that the EC is required to consider a third extension to the UK’s exit date, it will be hard for it to escape the conclusion that conditioning an extension upon the UK parliament’s approval of the Withdrawal Agreement which was concluded on 25 November 2018 is the only logical way in which it can comply with its obligations under paragraphs 1 and 2 of Article 50.
The European Union (Withdrawal) (No 2) Act 2019 is notably silent on the precise purposes for which, if needed, the UK parliament will use any extended period of time before the UK leaves the EU. The EC must now seize the initiative and exercise its power to grant an extension on Article 50(3) in a way which enables it to intervene more decisively in the question of whether the UK leaves the EU with or without a deal.