Later this week, the Prime Minister is expected to ask the European Council to extend Article 50. If the Governments of the 27 EU Member States unanimously agree to her request, the UK’s departure from the EU will be delayed. The Library has previously explained how that EU decision-making process will work. Common misconceptions have arisen as to the role of domestic legislation in this process. This Insight clarifies the role of domestic law in extending Article 50.


The UK has honoured its obligations as an EU Member State through a piece of legislation called the European Communities Act 1972. It gives effect in domestic law to obligations the UK owes in EU law. It provides that the UK “dynamically aligns” with EU law on an indefinite basis.

When the UK leaves the EU that arrangement will no longer be suitable. Unless – and to the extent that – a ratified Withdrawal Agreement provides otherwise, the UK would not have continuing rights and obligations under the EU Treaties. There would be nothing to “implement” in domestic law in the event of a no-deal exit. This is why the EU (Withdrawal) Act 2018 was passed. Its purpose was to create a legislative scheme that replaces the arrangements under the European Communities Act (ECA) for a post Brexit constitutional environment. While it would preserve a great deal of the substance of EU law in domestic law, it provides a new constitutional basis for it and it would end “dynamic” alignment between the two systems of law.

Getting the timing right – why it matters

These changes to domestic law need to take place in a coordinated manner and ideally at exactly the same time as the UK formally leaves the EU. This is necessary to provide legal certainty to individuals, businesses and other organisations whose activities are currently regulated (in whole or in part) by EU laws.

If these changes came in too early, the UK would run the risk of breaching its obligations as a Member State. Infringement proceedings could be brought against the UK before the Court of Justice of the EU. If these changes came into force too late, there would be a significant gap in UK law. People’s rights and obligations would be unclear as would their means of redress before the courts if they became a matter of legal dispute.

“Exit day” – the official switch-over

The legislative solution in the EU (Withdrawal) Act 2018 is to have one designated “switch-over” date: “exit day”. After this point (among other things) the ECA (and other EU-related legislation) is repealed and the new system of “retained EU law” comes into effect. Section 20(1) defines “exit day” as 29 March 2019 at 11pm GMT.

This date coincides with the date on which (by default) the EU treaties cease to apply to the UK. This follows the notification of intent to withdraw having been made on 29 March 2017. However, “exit day” is not formally linked to that date: it will not “automatically” update if (for whatever reason) the UK’s membership of the EU continues beyond 29 March 2019.

The domestic law definition of “exit day” does not affect when the UK leaves the EU. It only affects when the UK changes its laws to deal with the domestic consequences of EU exit.

By a similar sentiment, the UK does not leave the EU simply by repealing the European Communities Act 1972. Repeal of that Act would only place the UK in breach of its membership obligations if it had not already left. The role of UK domestic law in the operation of Article 50 is to determine whether the UK Government can or must start it (by notification) or stop it (by revocation). No more; no less.

Why might “exit day” need to be changed?

If an extension is agreed by the European Council with the UK Government, the “the day and time that the Treaties are to cease to apply to the United Kingdom” will be later than the definition of “exit day” in UK primary legislation.

In such a scenario the UK would continue to be a member of the EU – with all the resulting obligations in EU law. However, if the EU (Withdrawal) Act 2018 were to be brought fully into force, this would have the effect of repealing the ECA. Even though much of EU law would have been “converted” into UK law, no UK court could refer a case to the CJEU, many financial payments to the EU would be (domestically) unlawful, and UK law would not “keep pace” with subsequent developments in EU law. Moreover, the commencement regulations for the 2018 Act provide that the European Union Parliamentary Election Act 2002 is to be repealed “on exit day”. Unless “exit day” is updated, the UK would have no domestic legal basis for holding European Parliamentary elections in May 2019.

How can “exit day” be changed?

“Exit day” is defined in primary legislation. Changing it would therefore normally require further primary legislation. However the EU (Withdrawal) Act 2018specifically contemplated the possibility of an extension being sought and granted, and allows exit day’s definition to be changed in those circumstances by secondary legislation.

Section 20(4) allows a Minister of the Crown to change exit day provided that a draft statutory instrument has been laid before and approved by both the House of Commons and the House of Lords. However, it can only be used:

“to ensure that the day and time specified in the definition are the day and time that the Treaties are to cease to apply to the United Kingdom.”

In practice this means that an extension must first have been agreed to at EU level before any such regulations can be made to change the date. As the Government itself said in a written statement on Friday 15 March:

“It is expected that the EU will use the March European Council on the 21 and 22 March 2019 to consider and reach a decision on a request from the UK to extend the Article 50 period.

As soon as possible following agreement at the EU level we will bring forward the necessary legislation to amend the definition of exit day in domestic legislation. This statutory instrument will be laid, before it is made, under section 20(4) of the EU (Withdrawal) Act 2018.

This legislation is subject to the draft affirmative procedure and so would need to be actively approved in each House. The legislation would give effect to any agreement with the EU on an extension, so would not be laid before Parliament until that agreement had been reached.”

About the author: Graeme Cowie is a Senior Library Clerk at the House of Commons Library, specialising in Brexit.