In case Brexit has already happened, can it be reversed after a short time?

Legally, the answer is no, I think.

But I can imagine a situation where, during the first few days after Brexit, all participants unanimously agree it should not have happened.

It is at least possible that the first days after Brexit create a crisis that makes all agree it went horribly wrong, and dangerously so.

From the EU side, let us assume it recognizes the crisis and is willing to cooperate in any way that its laws allow.

If all relevant politicians of all parties in the UK would unanimously agree that it lead to a catastrophic crisis, and should be reverted at any cost - is that possible in any controlled way?

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    @VolkerSiegel With all due respect, your scenarios are wildly fantastical. The UK is not going to "uncontrollably descend down to a failed state" or "go to war with the EU" in the first few days after Brexit, even in the worst case scenario.
    – JBentley
    Commented Sep 15, 2019 at 11:03
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    @VolkerSiegel Ok, but I don't think it matters. The solutions for the UK rejoining the EU are the same regardless of the reasons for rejoining. Namely, joining via Article 49, or rewriting the rules via treaty change (as per the two answers). Coming up with more and more extreme scenarios is in my opinion just distracting from the question, which is really "how can the UK rejoin the EU after Brexit and/or how quickly can that be done?". Or to put it another way, taking your title question "Can Brexit be undone in an emegency?", an answer would be "Yes, the same way as in a non-emergency."
    – JBentley
    Commented Sep 15, 2019 at 11:14
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    Just about any agreement can be undone or recreated if all parties agree to do so, even when there are rules or laws standing in the way. But 4 rare things in politics are unanimous agreement, admitting to mistakes, speed and making exceptions.
    – NotThatGuy
    Commented Sep 15, 2019 at 11:47
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    Another -1 for fantasizing that Brexit is some unimaginable instant disaster.
    – RonJohn
    Commented Sep 16, 2019 at 20:13
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    @glglgl then we can hypothesize what would happen if John Bull and Athena come down from the clouds on the day after Brexit and restore the Empire and bring Ireland to heel. Point being that unless you want politics.SE to devolve into partisan fantasy, limits must be maintained on the level of fantasy.
    – RonJohn
    Commented Sep 17, 2019 at 8:26

4 Answers 4


"Can it happen"? Sure, the laws of the EU are set by the members of the EU, if the members want to change the rules they can. They can re-admit the UK or not. If there is a law against it, the EU can just change the law. With sufficient political will on both sides it is possible.

"Will it happen"? After years of causing problems, how likely is it that the political will would exist?

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    While I do agree with what you're saying, the answer would be a lot better with some background sources that support your argument. It also answers a question with another question "how likely is it that the political will would exist?", instead of explaining why there is or isn't a chance for the political will to exist. As is, it reads like a comment.
    – Peter
    Commented Sep 14, 2019 at 21:44
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    @Peter: That would be answering a different question. This question assumes the EU "recognizes the crisis and is willing to cooperate in any way that its laws allow." Changing the laws is allowed by the laws, so this is a complete answer.
    – Kevin
    Commented Sep 14, 2019 at 22:17
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    The EU cannot just change the laws that govern it. This would, at the very least, require votes in all the parliaments, possibly referenda in multiple countries, and would certainly result in legal challenges at the highest level in courts all over Europe. This would likely take longer than than the process for seeking membership by normal means. It would also require the UK to realign it's laws to the EU, the very issue they want to leave over (if you take the Brexiter talk at face value, which I personally don't). The practicalities make it impossible to implement quickly as well. Commented Sep 15, 2019 at 14:16
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    The commision can't change the Law, but neither the commision, nor the parliament is the EU. The EU is the union of the countries. By the consent of all the countries of the EU any EU treaty can be changed. However treaty change is not required to re-admit a country, only the approval of the European council.
    – James K
    Commented Sep 15, 2019 at 19:36
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    Considering that in 2017, Jean-Claude Junker told the German Newspaper "Bild" that "Britain will be made an example of", I don't think that the Political Will ever existed... Commented Sep 15, 2019 at 22:59

No. But the UK can apply for membership according to Article 49 of the Treaty on the European Union. This normally takes years. The article text:

Any European State which respects the values referred to in Article 2 and is committed to promoting them may apply to become a member of the Union. The European Parliament and national Parliaments shall be notified of this application. The applicant State shall address its application to the Council, which shall act unanimously after consulting the Commission and after receiving the consent of the European Parliament, which shall act by a majority of its component members. The conditions of eligibility agreed upon by the European Council shall be taken into account.

The conditions of admission and the adjustments to the Treaties on which the Union is founded, which such admission entails, shall be the subject of an agreement between the Member States and the applicant State. This agreement shall be submitted for ratification by all the contracting States in accordance with their respective constitutional requirements.

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    And then they will enter with much worse terms they had while they were in. As founding members, they had some special privileges, which they will not receive again if they apply in the future as a new member candidate.
    – vsz
    Commented Sep 15, 2019 at 13:57
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    @vsz UK was not a founding member of the EEG. Germany, France, Italy, Netherlands, Belgium and Luxembourg are.
    – Sjoerd
    Commented Sep 15, 2019 at 14:20
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    @vsz At one of the many treaty changes that introduces new elements, the UK asked for an opt-out. As did Denmark, and I think Ireland as well (and maybe others). But that's not the only way: The rebate was "earned" in 1984 when UK threatened to paralyze the EC with vetoes - everything requires unanimity at that time - until they got their rebate.
    – Sjoerd
    Commented Sep 15, 2019 at 14:37
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    @Sjoerd No privileges will be given. And the pound will have to go. Commented Sep 15, 2019 at 15:10
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    @MartinSchröder the way the "convergence critera" work make Euro membership effectively optional; countries have to sign up to "work towards" it, but not at any particular rate. Recently joined Croatia is still using the Kuna, for example. This is one of those things where the UK government spent a lot of time misleading people during the Scottish referendum and then found it backfired.
    – pjc50
    Commented Sep 15, 2019 at 15:42

The problem with "what if" is that anything goes.

If they find unobtanium under the hills of Wales which clearly would yield trillions of euro of profit every year but requires ten trillion euros to invest first which clearly requires an all European effort, you bet everyone would very, very quickly find which half of the toast is buttered. Amend the Lisbon treaty? That can be done in weeks if there is a concentrated will. Yes, you can run referendums if necessary extraordinarily quick if you really badly want to.

Lacking a miracle like that, what catastrophe can hit that would mould the will of some half a billion people into a single unit all of a sudden? Perhaps widespread, immediate threat of famine could do it but last I checked Britain was not exactly the breadbasket of Europe.

  • how long is a piece of string? Commented Sep 16, 2019 at 11:21
  • In the UK we are told that a new referendum would take at least nine months.
    – gnasher729
    Commented Sep 16, 2019 at 21:33
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    Even under current legislation it wouldn't (PPERA specifies a ten week minimum campaign period and there's no other relevant law) but if we are in fantasy land, laws can be amended really quick (see how fast some legislation went through both houses just the other week).
    – chx
    Commented Sep 16, 2019 at 21:46
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    Even assuming the unobtanium scenario, the UK might get those trillions as loan (or joint venture) from the US... In reality, rejoining the EU would require the UK population to no longer assume that the Polish plumbers are an existential (economical, of course) threat. Commented Sep 16, 2019 at 22:02

The answer is "no", but the UK would have a good chance of joining EFTA (the European Free Trade Association) quickly (the "Norway solution"). This would give the UK many of the benefits of being in the EU without the worst of the negatives.

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    This is speculation, and Norway has indicated they oppose this. Basically the UK's behavior in the EU has caused a wide distrust of the UK. If anything, they'd be admitted as a non-voting member.
    – MSalters
    Commented Sep 16, 2019 at 7:51
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    Disregarding the fact that, no, they won't have a good chance of joining EFTA, doing this would give the UK less benefits of being in the EU, with more of the negatives than they had as the special, privileged member that they were. Commented Sep 16, 2019 at 8:07

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