The two-year time limit stipulated in Article 50, argues Philip Allott, is wildly unrealistic: its drafters never anticipated that a large member state would ever leave the EU. In this legal opinion, he sets out how the ECJ could extend the withdrawal period, thereby allowing the UK to leave in an orderly fashion.

The UK’s scheduled withdrawal from the EU next March – quite possibly without a deal – has led to general legal confusion. It may be useful to identify legal aspects of the situation which are, in my opinion, beyond reasonable doubt. The underlying legal situation might now be irremediably corrupted, but it may still be worth setting out a legal opinion that could have been given at any time during the Article 50 process and which, in my view, still applies. One purpose of a framework legal opinion of this kind is to allow other people to express their own opinion on the same matters as precisely as possible.

1. The UK notification of intention to withdraw from the EU may be withdrawn at any time. It is a notification of intention to withdraw. It is not a notification of withdrawal, notwithstanding the erroneous title of the European Union (Notification of Withdrawal) Act 2017. (Section 1(1) of the Act is correct.) If the intention changes, the European Council could be so informed and the negotiation of a withdrawal agreement could cease. Many treaties contain a provision allowing for ‘notification of withdrawal’ by a contracting party (not including the word ‘intention’).

2. The period of negotiation of a withdrawal agreement can be extended beyond 29 March 2019. Article 50, paragraph 3, of the Treaty on European Union provides as follows. “The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.”

(a) Given the catastrophic consequences, in the UK and the EU and across the world, of a UK withdrawal without an agreement, it would surely be a grave breach of public responsibility on both sides to fail to extend the period of negotiation – a failure that could constitute a breach of UK public law and/or of EU law.

(b) The negotiation of international agreements on a large scale always takes many more than two years. A withdrawal agreement between the UK and the EU would affect every aspect of two vastly complex constitutional and substantive law systems, from the broadest to the most detailed levels, and the constitutional and substantive law systems of 27 other states, not to mention its worldwide effects.

(c) It could not possibly be expected to enter into force two years after the start of its negotiation, given that, to enter into force, it must be concluded by the European Council, with the consent of the European Parliament, subject to ratification by 28 states – processes that could typically take many years.

(d) Such a wildly unrealistic two-year time-limit suggests that the drafters of Article 50 had in mind that there was no realistic prospect that it would ever apply to one of the largest member states. One of the principal drafters has confirmed this.