Under the terms of the Northern Ireland Backstop, the UK (or at least Northern Ireland) would be obligated to broadly follow EU rules surrounding the Single Market and the Customs Union.

If, at some point in the future while the backstop is in effect, the EU decided to amend the treaties in relation to the SM or CU, would this require consent from the UK? If the UK refuses to give consent, would it invalidate the backstop, or can it be forced onto the UK anyway?

  • 1
    Why focus on treaty changes? There is no special rules about that as far as I know but major treaty changes are not likely for the foreseeable future and many treaty changes (even significant ones) would not directly impact the backstop. On the other hand, given the way the single market works, the backstop means that Northern Island has to track changes in secondary law (in particular EU directives). The EU enacts directives all the time and the UK would have no say in this.
    – Relaxed
    Commented Mar 16, 2019 at 21:45

2 Answers 2


No to both questions. It would be forced onto the UK anyway. And there's more to it than EU treaty changes. The backstop section in May's deal would basically subject:

  • Northern Ireland to new legislation passed in the EU, owing to the fact that Northern Ireland would stay aligned with the EU's internal market for e.g. food standards, etc.

  • The UK to new trade treaties passed by the EU and whatever else affects the customs union, owing to the fact that the UK in its entirety would stay in the customs union.

In both cases the UK (and NI) would have no say on paper. (In practice I can't imagine the EU not keeping the UK in the loop behind the scenes.)

That being said, several other points in case you're asking while wondering what to make of the backstop:

  • The reason there's a backstop to begin with is because of the Good Friday agreement. Had there not been a peace treaty that says there cannot be a hard border between Ireland and Northern Ireland, the backstop wouldn't have been necessary.

  • What the EU wanted originally was to only keep Northern Ireland in sync with the EU, in order to maintain an open border between NI and the ROI. Until late last year the EU had a red line whereby making the backstop apply to the UK in full was out of the question. May got a huge concession when the EU reversed its red line, and this led to the current deal.

  • The reason the EU is so dead set about the backstop is because not doing so would create an existential threat to the EU. The EU was created on the ashes of Europe after WW2, to perpetuate and defend peace across the continent. If it doesn't stand firm on defending the Good Friday agreement that Ireland (an EU member) passed with the UK, the EU would basically be sending a message that a) the EU doesn't stand behind its members and b) it's fine to fudge with peace treaties that affect EU members.

  • The backstop is a last resort thing. It's not supposed to come into effect unless negotiations break down completely or aren't completed by a certain date.


Also, if memory serves me well, there's some language in the treaty that gives the island of Great Britain a unilateral opt out -- so long as Northern Ireland remains in the backstop for as long as necessary. Or maybe there were only talks about it -- but if so I can't imagine why the EU would have rejected that. (I can't find the exact source or podcast where I came across this. A helpful reader will hopefully add a link in the comments or edit it into this answer.)


You're objecting in a comment that this doesn't actually answer the question, so let me make another point more explicit: the Irish backstop is completely unrelated to the UK's ability to influence treaties once it leaves.

The moment the UK is no longer part of the EU, is the moment where it no longer has any say on what's going on in the EU or on EU treaties. Period. Just like Norway or Switzerland, which align with parts of EU laws, without having any say on what goes on in the EU. (Not officially anyways. One might easily imagine some backchannel communications as a friendly courtesy.)

  • I'm referring specifically to the Treaty of the European Union, and amendments thereto. This answer doesn't appear to address this with any real references.
    – Joe C
    Commented Mar 16, 2019 at 16:03
  • While the EU does not want to use the backstop, the backstop would come into effect if nothing else is agreed by the end of the transition period. Why should the next two years of negotiation run any better than the last two years?
    – o.m.
    Commented Mar 16, 2019 at 17:23
  • @o.m.: Very personally I'd expect the backstop to kick in for a very long duration from lack of a better option for the UK. But the ERG apparently believes that the UK can ride a magical unicorn to India and other Commonwealth countries and sign trade deals with them that will benefit the UK. Also, remember Liam Fox's EU trade deal after Brexit should be "easiest in history" to get comment? Commented Mar 16, 2019 at 21:18
  • The treaty does not say there cannot be a border though.
    – user19831
    Commented Mar 17, 2019 at 13:28
  • @o.m. and the total failure of the British Parliament is exactly the reason why the Backstop is needed in the first place!
    – Josef
    Commented Mar 19, 2019 at 14:48

If, at some point in the future while the backstop is in effect, the EU decided to amend the treaties in relation to the SM or CU, would this require consent from the UK?

It would somewhat depend on the scope:

  • The EU passes a new regulation or directive on widgets via the ordinary legislative procedure (or any of its other "regular" legislative processes) - The UK is out of luck. This would not constitute "amend[ing] the treaties" of the EU in the first place, so the EU would just make the decision without consulting the UK. If the EU is feeling generous, it might ask the UK for its views, but it would certainly be under no obligation to do so.
  • The EU dramatically restructures itself, like it did with the Lisbon Treaty - This is rather improbable to begin with. As far as I'm aware, the EU currently has no intention of such a thing. Depending on the extent of the reorganization, parts of the backstop might need to be renegotiated or reworded. This would be an incredibly delicate process, both politically and legally, and it seems unlikely that either the EU or the UK would be pleased to be in this situation unless there were no alternative. Ultimately, the European Court of Justice does have jurisdiction over the backstop and could resolve any intractable legal issues, provided that the reorganization did not abolish the ECJ altogether.*
  • Something in between those extremes - Politics is messy, and it is difficult to forecast the exact result of every possible eventuality. It's somewhat likely that the UK and the EU would try to reach an agreement without the ECJ's involvement, but the extent to which each side is willing to negotiate will greatly depend on many complicated political and legal factors, and it is not at all obvious that there are any "bright lines" here. However, in general, the UK is not likely to get much out of this process except to the extent that the change directly impacts the terms of the backstop in particular (as opposed to, for example, the UK economy as a whole). As with the previous case, the ECJ would adjudicate disagreements.

* If the EU did abolish the ECJ altogether, and also failed to designate a replacement, it would no longer be the EU as we know it, and I have no idea what would happen next.

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