As I understand, one of the sticking points in the Brexit negotiations has been Britain's level of obligation to a proposed customs union backstop.

I understand also that this is essentially a transitional arrangement to keep the entirety of the UK in a de-facto customs union and single market, to avoid either the physical division of Ireland or the political division of the United Kingdom (the clue being in the name).

What I don't think I fully appreciate is why the EU objects to the UK having the power to walk away from a backstop before a new arrangement is found. Is the reason economic - because it creates uncertainty? Is the reason diplomatic - because it undermines the EU's position in the subsequent talks? Or is there another subtlety I haven't grasped?

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    Comments deleted. Please don't use comments to answer the question. If you would like to answer, please post a real answer.
    – Philipp
    Commented Nov 15, 2018 at 14:14
  • Your question implies that a new arrangement is certain to be agreed. Would you like to modify your question, to clarify the possibility (some would say likelihood) that no such arrangement ever emerges, or in light of the fact that it took Canada sixteen years to negotiate such an arrangement? No doubt it would suit Teresa May to kick the problem into the long grass, but her political enemies will not want to wait so long to be rid of her.
    – Ed999
    Commented Nov 18, 2018 at 3:11
  • @Ed999 That is why I called it a "proposed" Irish / customs union backstop. Commented Nov 19, 2018 at 11:59

9 Answers 9


The EU is acting in the interests of the remaining 27 members. In this case it is specifically acting in the interests and on the instructions of the Republic of Ireland, which opposes a hard border under any circumstances.

The Republic of Ireland, and so the EU, are opposed to the UK having the ability to unilaterally exit the backstop as it removes any power they (IRE & EU) have to ensure that a hard border is avoided.

The European council - which is the body containing the heads of government of each of the EU countries - unanimously adopted a set of negotiating guidelines at a meeting in May 2017. These guidelines covered the border in Ireland. Subsequently, Michel Barnier et al have followed these guidelines closely, whilst leading Irish politicians, including PM Leo Varadkar, have been explicit in their desire for and support of the guidelines.

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    @JamesMoore But it is perfectly normal, and in everyday currency,to use the term "Republic of Ireland", so as to distinguish that sovereign territory from Northern Ireland, and to be clear that one is not speaking of the island of Ireland as a whole. In the same way it used to be accepted, for clarity's sake to speak of East Germany and West Germany, even though they were not the names of the countries concerned. Similarly it is the case still with North Korea and South Korea - they are not their official names.
    – WS2
    Commented Nov 15, 2018 at 0:22
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    @JamesMoore It's officially ok to refer to it as the Republic Of Ireland. And unofficially it makes this answer less confusing to make a clear distinction between the Republic Of Ireland, Northern Ireland, and the island of Ireland. en.wikipedia.org/wiki/Republic_of_Ireland_Act_1948
    – Schwern
    Commented Nov 15, 2018 at 0:26
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    @alephzero A hard border would violate one of the key tenants of the Good Friday Agreement that ended the Troubles and has saved hundreds of lives. The EU is protecting its members, that's what a union is for. en.wikipedia.org/wiki/Good_Friday_Agreement
    – Schwern
    Commented Nov 15, 2018 at 0:30
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    While this answer is technically true, I think it rather avoids the main issue, which is the Good Friday Agreement. The GFA requires that there be no hard border between Northern Ireland and the Republic of Ireland by law, and the backstop ensures that this remains the case.
    – walrus
    Commented Nov 17, 2018 at 19:41
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    @walrus To expand further: the EU is not party to the Good Friday Agreement and so has no direct obligations itself to avoid a hard border. However, the Republic of Ireland is and so they have instructed the EU to pursue an agreement which satisfies their (Republic of Ireland) obligations.
    – stuart10
    Commented Nov 19, 2018 at 8:34

What's so important about the border? It's because dividing Ireland means an open invitation for a civil war again. The Troubles may or may not materialize again, but everybody would rather play it safe than find out.

EU doesn't want that. UK can't really be trusted they won't break the agreement that ended The Troubles, because some of the factions in power in UK act like they don't care about peace in Ireland.

Tying the backstop to the rest of the deal means that the deal is held hostage by the backstop. It basically sours the pot for the UK in case they consider bringing civil war back to Ireland. That's what makes it so attractive for Ireland, EU, and some in UK. Without the connection, UK could bring hard border back and retain eg. ability to import medicines from EU. With the connection, UK gets hit twice: once with risk inherent to hard border and secondly, with cutting down economic ties to EU (what makes the risk of eventual civil war even costlier, eg. without medicines to patch up SAS soldiers wounded in NI firefights).

Assuming that UK doesn't actually want hard border, they objectively lose nothing. The only thing they lose is face, because voters view it as giving up some options. And that's way more than it sounds, because the whole Brexit is about giving UK some options.

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    My personal opinion is that keeping the status quo of NI is possible only when both UK and Éire are parts of one, bigger thing. This way Republicans can act like they're in Éire, Unionists can act like they're in UK and everybody's happy. The very idea of Brexit is against peace in NI. UK government has demonstrated irresponsibility in this matter by allowing the referendum, they've played "all in" being sure to win - and lost. Twice, if one counts the extra elections. Now, nobody can trust UK to do the right thing, and this makes negotiations harder.
    – Agent_L
    Commented Nov 14, 2018 at 16:10
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    Hard to imagine describing NI/Ireland troubles resurgence as "a civil war" when they are already divided i.e. not the same state Commented Nov 15, 2018 at 11:39
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    @LightnessRacesinOrbit The Troubles happened inside Northern Ireland. It's "NI people who want to join Republic" vs "NI people who want to remain in UK". Dublin is not a side in this conflict. Hence I used the term "civil war". The "civil" part is unquestionable, although I exaggerated the "war" part.
    – Agent_L
    Commented Nov 15, 2018 at 12:14
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    Oh, right, civil war within NI. Sorry that makes sense. Commented Nov 15, 2018 at 13:37
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    @LightnessRacesinOrbit Well, by definition, civil war in NI = civil war in UK. Commented Nov 15, 2018 at 23:56

If either party can walk away unilaterally from part of an agreement, then what use is the negotiation in the first place? In this instance if the UK walks away from the backstop proposals unilaterally, this means there would not be a replacement agreement to deal with the issue of the Irish Border and the Good Friday Agreement (GFA), because by definition if there was such an agreement it would be bilateral.

The EU is concerned that allowing the UK to unilaterally change a part of the deal leaves the island of Ireland in a constant limbo with no clear picture of what state the border will be in next year, or potentially next week. Any change to conditions on the Irish Border risk the GFA and if done unilaterally would lead to a chaotic situation where it would be unclear under what principals goods and/or people could move across the NI/Eire border.

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    Not sure what the risk is "next week"? Commented Nov 15, 2018 at 11:38
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    @LightnessRacesinOrbit it means that you can't predict what the situation will be even over a short period of time.
    – Jontia
    Commented Nov 15, 2018 at 11:43
  • The UK is in the EU until next year no matter what Commented Nov 15, 2018 at 13:36
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    @LightnessRacesinOrbit The statement is phrased from a future point of view, not necessarily right his instant. "Next week" doesn't mean "the week of November 19th", but rather "at some point in the future, after Brexit has occurred, it would be impossible to predict the situation a week in advance, because the UK is allowed to walk away from the agreement on a whim."
    – amalloy
    Commented Nov 15, 2018 at 20:02
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    @amalloy Okay, makes sense Commented Nov 16, 2018 at 10:48

Why is the EU concerned about the UK “unilaterally withdrawing” from a backstop

I don't think that is an accurate description of the issue.


UK Pro-Brexit MPs want a backstop to have a time limit or clear exit route. This is because they believe that locking the UK into the EU's customs union indefinitely would mean the UK could not have a meaningful independent trade policy.

The Irish government assert that the backstop cannot have an arbitrary end point but must apply unless and until some other political or technical development means it is no longer needed.

(paraphrased from https://www.bbc.co.uk/news/uk-northern-ireland-politics-44615404 - my emphasis)

Hard Borders

The UK government has said it does not want a hard border in the island of Ireland, so there is general agreement in the whole of the EU on that fundamental point. So far as I know, no major UK political party has proposed a hard border in the island of Ireland.

The BBC report

There is widespread agreement among UK politicians that there should be no return to what they call a hard border and that the Common Travel Area (CTA) should be maintained after Brexit.

Keeping agreements

The issue isn't whether the current or future UK government can be trusted to keep agreements it or it's predecessors have made.

If you don't trust someone to keep an agreement, you generally don't solve the trust issue by negotiating another agreement with them.

The point is to make sure that any agreement clearly and unambiguously meets the concerns of all parties to that agreement.

Unilateral withdrawal

So far as I know, governments only unilaterally withdraw from an agreement if the agreement provides for them to do so (but see Vienna convention below). For example article 50 of the treaty of Lisbon provides a mechanism by which an EU member state can arbitrarily and unilaterally withdraw from the union. It says "Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements"

So far as I can discern, the main pro-Brexit viewpoint is not that there should be a unilateral withdrawal clause to the backstop but that there should be a clause which describes the pre-agreed circumstances under which the backstop would become no longer needed to meet UK or IE concerns (e.g. perhaps a clear definition meeting the "some other political or technical development" of the Irish government's position).

The Irish Times puts it thus:

The breakthrough came with an agreement on a review mechanism that would determine when the backstop is no longer necessary to ensure that the Border remains open after Brexit.

The backstop is an insurance policy written into the withdrawal agreement guaranteeing no harder border on the island of Ireland. It would only be used as a last resort or the default option if the EU and UK cannot reach an overarching free trade deal that would make trade so frictionless that there would be no border between the EU and the UK, including on the frontier between Northern Ireland and the Republic.

Vienna convention

The Vienna Convention on the Law of Treaties states where a party wants to withdraw unilaterally from a treaty that is silent on secession, there are only two cases where withdrawal is allowed: where all parties recognise an informal right to do so and where the situation has changed so drastically, that the obligations of a signatory have been radically transformed.

  • The trouble with a term like "hard border" is it means different things to different people. Does a border with no permanent barriers but number plate scanners and targetted customs inspections count as a "hard border"? Commented Nov 16, 2018 at 15:13
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    @PeterGreen: The term is essentially undefined. Some Irish politicians say "harder border" rather than "hard border". So far as I can tell, the border arrangements are not defined or even mentioned in the 1998 British-Irish Agreement (also known as The Belfast Agreement / The Good Friday Agreement) Commented Nov 16, 2018 at 15:31
  • The term is generally understood to mean no return to the old days of border checkpoints. Any purely electronic measures relating to the export/import of goods would not be considered a return to the bad old days.
    – Ed999
    Commented Nov 18, 2018 at 2:54
  • "the “Smart Border 2.0” proposals do involve physical infrastructure and border guards" but the meaning of "hard border" should probably be a separate question Commented Nov 18, 2018 at 12:33

All parties want to avoid a hard border in Ireland, but the problem is that the UK also wants to be free to trade with anyone they want, even if that trade violates EU rules.

If the EU agreed to allow the UK to do this, and also allowed for there to be no hard border in Ireland, it would end up compromising the EU borders. The UK would be free to import goods from anywhere in the world, and then export those goods to the EU. The UK would essentially become a backdoor into the EU. It's pretty obvious that they cannot allow this situation to happen.

The UK want to have their cake and eat it. They want to both be part of the EU (no hard border in Ireland), and not part of the EU (free to make their own trade rules). These two aims are in direct opposition.

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    +1, but I would add that there are potential solutions, e.g., the proposal to place a customs border between Northern Ireland and the rest of the UK. Or Northern Ireland could become an independent nation, or even part of the Republic. It's just that the UK don't like those ideas either, and to be fair, they would probably result in just about as much trouble as breaking the Good Friday Agreement would. Commented Nov 15, 2018 at 20:53
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    "simple matter to check goods arriving by ship in Rotterdam from Ireland" : no, that's against EU free movement of goods! The whole point of the EU is the ability to do that without checks.
    – pjc50
    Commented Nov 18, 2018 at 12:21
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    @Ed999 That's not a solution, let alone an easy one, that's wishing Ireland away. Which is a common theme in some conservative commentary nowadays but that's incredibly arrogant and deeply ironic when Brexit supposedly is about the British deciding for themselves free from meddling from the outside. What it really is about is the British (or the English really) deciding for the Irish and the whole of the EU, not about any concern for democracy or respect...
    – Relaxed
    Commented Nov 18, 2018 at 19:34
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    @Ed999 "to check goods arriving by ship from Ireland" essentially means a border between Ireland and mainland EU, which is not a matter the UK has a say in. It's akin to suggesting that US could open the border between Mexico and TX and just check the papers on inner TX borders. Commented Nov 19, 2018 at 10:16
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    @Ed999, it's not that the UK wants to violate EU rules for some nefarious purpose. If the UK wants to import US beef for example,that's an issue for them but the EU doesn't want to allow it into their food chain. That means either border checks between mainland Britain and the island of Ireland (unionists won't like that), border checks between NI and ROI (nobody will like that) or border checks between ROI and the rest of the EU. That last proposal would mean that Brexit is achieved at the expense of ROI trade with the EU, why would ROI volunteer to take that hit even if it were legal?
    – PhilDin
    Commented Nov 19, 2018 at 11:43

The UK's unwritten constitution has the provision that current parliament cannot tie the hands of future ones in most cases. Therefore any promises made by the current government regarding the Irish border can only be enforced by international treaty, not merely by UK law (which can be repealed/amended unilaterally by future governments).

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    Parliaments, not governments. It’s Parliament that is sovereign, not the government.
    – Mike Scott
    Commented Nov 15, 2018 at 14:50
  • Side note: The provision is written down in The Law of the Constitution (1885), pp 39-40. Commented Nov 16, 2018 at 14:41

Many important points have already been made but one thing missing is that the backstop is emphatically not a transitional agreement. It's a fallback position if at some point in the future the arrangements between the UK and the EU fail to guarantee a border without physical infrastructure. It would not come into force in March 2019 when UK-Irish trade is still covered by the so-called “transition period” rules. In fact, it's not supposed to ever come into force, if you believe the claims that it should be possible to agree to some trade agreement that would deal with the border issue before the end of the transition period.

  • But who really believes the claims? Are the UK's politicians really so stupid that they would believe that the EU will act in good faith, when the EU is so transparently desperate to prevent the UK from leaving?
    – Ed999
    Commented Nov 18, 2018 at 2:29
  • The EU is extremely good at sticking to its own rules and agreements. What kind of "not good faith" did you mean?
    – pjc50
    Commented Nov 18, 2018 at 12:23
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    @Ed999 I do not believe the EU is desperate or even interested in preventing the UK from leaving at this point. But that's neither here nor there, I don't think anybody believes these claims, pro-Brexit politicians just make them when it's expedient and then act as if they did not believe them (for example by being very concerned about the backstop).
    – Relaxed
    Commented Nov 18, 2018 at 19:22
  • @ed999 Frankly from an EU perspective the UK has been always a big pain in the neck, always wanting exceptions, special deals, rebates etc. It is one of the big limiting factors in the ability to address many of the shortcomings of the EU. Commented Nov 19, 2018 at 10:35
  • The EU might (or might not) stick to terms it has agreed. That is not the point. The issue is whether the EU will act in good faith, if the UK was fool enough to sign an agreement that the UK and EU will use their best endeavours to agree terms for future trade. It is not a question of honouring a set of agreed rules, but instead is a matter of agreeing a set of rules. The EU wants the UK to sign an agreement that will apply until a further agreement is made, but will the EU ever make that further agreement? Clearly, it won't, as the initial deal locks the UK into the EU's rules forever.
    – Ed999
    Commented Nov 28, 2018 at 2:33

The EU is simply insisting that the UK stick to other commitments that it has made to EU members, in this case the Good Friday Agreement with Ireland. That agreement can only be modified with the consent of the voters of both the Republic of Ireland and Northern Ireland, the former of whom didn’t vote on Brexit and the latter of whom voted against it. If the Brexiters want a looser relationship with the EU while keeping the UK intact, then democracy requires that they convince those voters, not just the voters of England and Wales. Since they haven’t done so, then the UK must stay aligned with the EU in many ways to enable the border to stay open.

  • I'm not sure it would make any difference if Northern Ireland had voted for Brexit; the Irish republicans would presumably still demand that the GFA be enforced. Commented Nov 15, 2018 at 20:57
  • The EU proposal is transparently an attempt to break up the United Kingdom, by splitting off Northern Ireland. This is unacceptable to the politicians in London and in Belfast. Hardly surprising. But it demonstrates the degree of bad faith which the EU is willing to employ.
    – Ed999
    Commented Nov 18, 2018 at 2:35
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    @Ed999 No, the EU isn’t trying to break up the UK. It would be perfectly happy for the whole UK to stay in the customs union and single market, or indeed in the EU. What is your counter-proposal to comply with the Good Friday Agreement while protecting the EU from unauthorised imports from the UK, without invoking magic technology that isn’t currently used anywhere in the world?
    – Mike Scott
    Commented Nov 18, 2018 at 7:10
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    @ed999 The agreement is an agreement between two parties. The problem is that the hard Brexiteers don't care about Northern Ireland and only want extreme deregulation. If there is any breaking up it is due to the cake-and-eat-it approach (publicly) used creating large friction in UK politics, possibly leading to a break in both the conservative party and the UK (if NI goes it is likely that Schotland goes as well, at least Charles will be able to stay the Prince of Wales). Commented Nov 19, 2018 at 10:30
  • @Ed999 Three parties, not two. It needed the consent of the Irish people, the Northern Irish people and the UK government.
    – Mike Scott
    Commented Nov 19, 2018 at 10:37

It is an open question whether the Irish Republic can remain in the EU, when the UK is not in it.

In the 1970s, the Republic found it necessary to follow the UK into the EEC, on January 1st, 1973. The UK is the Republic's most important trading partner, and the Republic and the UK had a common currency until 1979.

Now the Irish border is a concern, and the only possible solution is not to have one. But this means the Irish government may have to bow to the necessities of history and follow the UK out. One out, all out.

The Irish Free State must once again become free.



The Republic and the UK are both committed to the Good Friday Agreement, whereby there is no 'hard' border, i.e. no physical checkpoints.

One method of achieving this is for the EU to be removed from the equation, so that the UK and the Republic can resolve the matter bi-laterally. This requires the Dublin government to make a bold move, and leave the EU.

There is no disagreement between London and Dublin; the Good Friday Agreement has been long in effect. The EU is now part of the problem, and so the next move is up to Dublin. But so far they have not yet recognised the changed political and economic situation they find themselves in.

The EU is unhappy about this possibility: all of its manoeuvering is designed to edge the situation away from this, mainly by seeking to control the UK's actions in perpetuity, by locking the UK into an agreement with no exit provisions, in which true control of the border will be handled (permanently) by Brussels.

The security situation in Ireland can only work if the Republic and Northern Ireland are both on the same side, and that includes the same side of the Brexit arrangements. It only works if both states are in the Eu, or both are out of the EU. It won't work with interference from Brussels: there is no squaring the circle if the EU is free to impose its arbitrary rules, full of conditions that simply can't be met.

An end to EU interference in the problem is a sine qua non of future progress.

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    This does not appear to be a popular idea in the Republic. Commented Nov 17, 2018 at 1:08
  • But a few years of economic chaos in the Republic once the UK has left the EU may lead to a desire to restore the more beneficial economic arrangements which existed between Eire and the UK prior to 1973.
    – Ed999
    Commented Nov 18, 2018 at 2:39
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    There is zero popularity for this in Ireland, the chaos is going to be on the UK side, Ireland is an extremely different country from 1973, Ireland already has free trade with the UK, and its own Common Travel Area, and it's far more likely that NI will vote to rejoin the Republic.
    – pjc50
    Commented Nov 18, 2018 at 12:28
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    That's an interesting perspective and not entirely implausible. The anti-EU conspiracy theory is however entirely unwarranted, the people most interested in preventing that outcome are the Irish themselves, not the rest of the EU. If Ireland is in fact forced out of the EU and in a close association with Britain, it would not be because it's particularly desirable but because the UK (and not the EU!) is once again imposing arbitrary rules on others. Which is exactly what the demands around Brexit amount to, no matter how strongly the English wish to portray themselves as victims.
    – Relaxed
    Commented Nov 18, 2018 at 19:28
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    @Ed999 No one can make an unconditional offer of a free trade deal. Suppose Ireland starts to heavily subsidise its manufacturing industry to allow it to undercut UK manufacturers? Suppose it relaxes its environmental standards? Suppose it decides to grant citizenship to a million refugees on condition that they relocate to the UK? Free trade deals have to be full of rules and regulations and restrictions.
    – Mike Scott
    Commented Nov 19, 2018 at 10:41

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