Just today (March 21st 2017), the news came out around the web that Theresa May will trigger Article 50 (Brexit) on March 29th:

The UK will begin official divorce proceedings with the European Union on March 29, prime minister Theresa May's spokesperson has announced. — Ars Technica

However, it is my understanding that the Supreme Court asserted Theresa May was not allowed to do this (warning: there's an autoplaying video on that page), and that it was a matter for the entire parliament to decide.

In a joint judgment of the majority, the Supreme Court holds that an Act of Parliament is required to authorise ministers to give Notice of the decision of the UK to withdraw from the European Union

What's going on? Did something occur in the meantime that reversed this decision? Is Theresa May attempting to get parliament's agreement on that date, or is something else going on?

  • I believe that she passed it while still complying with the Court's decision - that is by not, to quote the article, "bypassing MPs and peers". Writing this as a comment because origimbo's answer is basically correct.
    – Boblicon
    Mar 20, 2017 at 14:18
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    The UK supreme court does not say May can't do it, it says she can't do it without MP approval. She got MP approval, so now she can do it. Mar 20, 2017 at 15:28
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    Important comment was that there was at least a theoretical possibility of the Brexit bill failing or being drastically modified by the democratically elected representatives. But I really don't know why May bothered to fight the court case rather than do it in this traditional Parliamentary manner.
    – pjc50
    Mar 20, 2017 at 16:46
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    Choosing March 29th seems odd. Surely it would have been more dramatic to go for March 25th - the 60th anniversary of the signing of the Treaty of Rome. But I suppose nobody on board the Brussels gravy-train would be in the office on a Saturday!
    – alephzero
    Mar 21, 2017 at 18:03
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    @alephzero Doing it on the anniversary would widely be regarded as an unfriendly act. You don't want to do that to a party you will need to negotiate with about quite serious matters.
    – Jens
    Mar 22, 2017 at 8:05

3 Answers 3


@origimbo's answer is completely correct and accurate. I would just like to go into the details of the Supreme Court ruling and what the UK Parliament has done.

Supreme Court ruling

Basically, the Supreme Court has ruled that as seen in this article by The Telegraph.

Supreme Court justices ruled, by a majority of eight to three, that Prime Minister Theresa May cannot lawfully bypass MPs and peers by using the royal prerogative to trigger Article 50 of the Lisbon Treaty and start the two-year process of negotiating the UK's divorce from its EU partners.

[ ... ]

A one-line Bill is expected to be drawn up and debated in Parliament, and Mrs May will be hoping that if that is the case, the Bill can go through the Commons and the Lords swiftly before becoming law as an Act of Parliament.

Actions taken by the government

So, the government has complied and Prime Minister Theresa May published the Brexit bill on 26 January 2017.

Text of the Bill:

1   Power to notify withdrawal from the EU

(1)  The Prime Minister may notify, under Article 50(2) of the Treaty on European Union, the United Kingdom’s intention to withdraw from the EU.
(2)  This section has effect despite any provision made by or under the European Communities Act 1972 or any other enactment.

The bill was then passed in both Houses of Parliament unamended for enactment by royal assent, which was given on 16 March 2017.


The European Union (Notification of Withdrawal) Act 2017 received royal assent on March 16th 2017. Since this bill passed both houses and has become law, the constitutional requirements for parliamentary assent that the Supreme court decision considered necessary have been met.

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    The Act has now been added to the "official" online legislation database: legislation.gov.uk/ukpga/2017/9/contents/enacted/data.htm Mar 20, 2017 at 14:44
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    In other words, Parliament decided, as required. Mar 20, 2017 at 14:58
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    @DavidRicherby Parliament didn't decide, as required. Parliament decided to let the Prime Minister decide to leave the EU, which meets the requirements of the Supreme Court decision because it explicitly gave the power to the Prime Minister notwithstanding the status of the European Communities Act 1972.
    – gsnedders
    Mar 20, 2017 at 17:54

To add a bit more (I read the full rulings which are interesting), the supreme court didn't say Theresa May (i.e., the government based on the prime minister's wish) could not trigger article 50.

What they said was, the government (and in the old days, the King) could not take a step that would affect people's legal rights without parliament's clear approval, and that this was such a step - so May would have to ask parliament to give its approval and couldn't just go ahead without it. Which after a bit of debate, they did.

The legal dispute in court was about two issues: (1) whether or not it could be said that parliament had given its approval already, and (2) if it hadn't, did it need to.

As background, there are some actions that the King - (which in modern times also includes the King or Queen's government led by his/her Prime Minister) used to be able to take just because he was King, without anyone else being asked (the "Royal Prerogative"), and other actions he/she can't take because it's Parliament that has the right to say yes or no , not the King/Queen (or his/her government).

So the real question behind the case - which gave it its legal importance - was simply, would triggering article 50 after a referendum that Parliament had approved but not said specifically what would happen if people voted 'yes', be (1) an action in the first group, where the King/Queen/government could do it without asking parliament, or (2) an action in the second group, where they could not do it until parliament specifically said "The King/Queen/government is authorised to trigger article 50" - and, if it was in the second group, had parliament effectively said "go ahead" already or hadn't they.

Examples of the kinds of questions involved in the decision were - does parliament agreeing to hold a referendum, also count legally as its agreement to do what the referendum says? How was parliament's approval handled in other UK referendums? Is leaving also implied in the EU treaties, so that in agreeing to endorse the EEC/EU treaties, parliament had also implicitly agreed they could be withdrawn at some future time if the government so desired? Would withdrawal actually change the legal rights of British citizens, or was that technically not a direct "effect" of the act of withdrawal itself? And so on.

  • Very clear explanation.
    – TripeHound
    Mar 22, 2017 at 8:24

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