Article 50 of the Lisbon Treaty says:

  1. Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.

What are the UK's constitutional requirements in this regard?

Update 3 July 2016

London law firm Mishcon de Reya is preparing legal action to clarify this issue. Their press release says "Legal steps have been taken to ensure the UK Government will not trigger the procedure for withdrawal from the EU without an Act of Parliament."

Blogger Jack of Kent surmises that they are seeking a "Declaration":

A good guess that it is for a “Declaration” on what Article 50(1) requires as a matter of English (and Welsh) law. A “Declaration” is a discretionary remedy of the courts ... when the correct legal position on something ... needs to be established.

An earlier-filed case has emerged: http://www.theguardian.com/politics/2016/jul/05/deadline-approaches-government-response-brexit-legal-challenge-article-50

More on this issue: http://www.independent.co.uk/news/uk/politics/in-full-the-letter-from-1000-lawyers-to-david-cameron-over-eu-referendum-brexit-legality-a7130226.html


3 Answers 3


In the UK, parliament is sovereign. Parliament has exercised its power by passing a bill to hold a referendum. The result of the referendum now gives the government the authority to act to leave the EU.

The constitution of the UK, based as it is on statute law, common law and tradition, gives final authority in constitutional matters to parliament. There is a (quite recent) tradition that in matters of significant change to the constitution, the people should be consulted, generally by referendum.

However if authorised by parliament or by a referendum, the decision to invoke article 50 is a matter for the executive, Ie the cabinet and the prime minister. This power follows from the general ability of the executive to form treaties and enact foreign policy, and derives ultimately from the powers of the monarch.

  • 1
    But isn't the referendum "purely advisory"? independent.co.uk/news/uk/politics/…
    – A E
    Jun 29, 2016 at 21:23
  • 1
    That a bit of rhetoric. It suggests it carries little weight. Insofar as the uk constitution is based on tradition, there is no tradition for ignoring the results of a referendum. However, this is the first time a referendum has both 1) indicated a change in the status quo and 2) not had the support of the government. So we are in unknown territory.
    – James K
    Jun 29, 2016 at 21:39
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    @JamesKilfiger As for article 50, that is just part of the picture. Invoking it only addresses our exit within the rules of the EU. To actually exit we need to address the situation within the UK, by repealing the Acts of Parliament by which we joined. Only parliament can do that. See for example the choice of wording used on the Parliament website: "give parliamentary assent to Britain's membership of the EEC" and "Britain's agreement to the Treaty received parliamentary approval". The precedent for such matters is to have Parliament's approval.
    – JBentley
    Jul 4, 2016 at 8:46

Today's decision in the High Court is that the government does not have the power to trigger Article 50 and withdraw the UK from the EU without the consent of Parliament.

R (Miller) -V- Secretary of State for Exiting the European Union [2016] EWHC 2768 (Admin)

The court does not accept the argument put forward by the Government. There is nothing in the text of the 1972 Act to support it.

In the judgment of the court the argument is contrary both to the language used by Parliament in the 1972 Act and to the fundamental constitutional principles of the sovereignty of Parliament and the absence of any entitlement on the part of the Crown to change domestic law by the exercise of its prerogative powers. The court expressly accepts the principal argument of the claimants.

For the reasons set out in the judgment, we decide that the Government does not have power under the Crown’s prerogative to give notice pursuant to Article 50 for the UK to withdraw from the European Union.

Summary: R (Miller) -V- Secretary of State for Exiting the European Union

An appeal to the Supreme Court is expected.


Well for a start the UK doesn't have a 'constitution' as such. The result of the referendum is not legally binding in terms of whether it is enacted upon or not. However, the EU are now looking to trigger Article 50 on our behalf because at earliest it doesn't look like it would be set in motion until October/November and this doesn't sit well with the EU. It would set a bad precedent where a country may then do a similar action in order to hold the EU to ransom regarding trade agreements and so forth.

  • 4
    Can you explain how the EU could trigger Article 50 on the UK's behalf and provide a link to the source that indicates that the EU are 'looking' to trigger it?
    – BeaglesEnd
    Jun 28, 2016 at 14:33
  • 5
    I don't think the EU can trigger Article 50 on the UK's behalf.
    – gerrit
    Jun 28, 2016 at 15:24
  • Also: "The German foreign minister, Frank-Walter Steinmeier, said on Saturday after meeting counterparts from the five other EU founding states: “We say here together that this process must start as soon as possible.” Earlier, Jean-Claude Juncker, the EU commission president, said: “It doesn’t make any sense to wait until October to try and negotiate the terms of their departure. I would like to get started immediately,” he said." theguardian.com/politics/2016/jun/25/… Jun 29, 2016 at 8:57
  • 1
    @CharlieAllen Quoting a EU politician who "would like" to get started immediately doesn't mean the EU can trigger Article 50 for us. The Guardian article you linked to even opens with, "they cannot compel UK to invoke article 50 ". The first link you gave is just some comment on Twitter - hardly a credible source.
    – JBentley
    Jul 4, 2016 at 8:50

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