# Brexit: What if the United Kingdom accelerated its own break-up… to Europe’s benefit?

- Author(s) : Lilà Schwartz
- Published : 2026-10-26
- Updated : 2026-10-26
- Publisher: PromethEUs, European federalist think tank (https://prometheus-euro.eu)
- Source : https://prometheus-euro.eu/en/news/brexit-what-if-the-united-kingdom-accelerated-its-own-break-up-to-europe-s-benefit

> Ten years after the Brexit referendum, the future of the United Kingdom is once again the subject of debate. On 14 September 2026, the SNP, Plaid Cymru and Sinn Féin signed a memorandum calling for closer cooperation and for constitutional change to be facilitated in Scotland and Wales, as well as in the context of Irish reunification. Although these movements advocate distinct projects, their rapprochement raises a major European question: could Brexit paradoxically pave the way for a new round of European Union enlargement?

## Key takeaways

- On 14 September 2026, the SNP, Plaid Cymru, and Sinn Féin signed a memorandum in Cardiff to coordinate their constitutional steps and promote a return to the European Union.
- Legal hurdles remain varied: Scotland and Wales depend on legislative approval from Westminster (confirmed by the Supreme Court in 2022 for Scotland), whereas Northern Ireland has a dedicated democratic framework under the Good Friday Agreement.
- EU accession would follow distinct pathways: an independent Scotland and Wales would need to go through the full Article 49 TEU procedure, whereas Irish reunification would automatically integrate the entire island without a new application.
- Public support for constitutional change varies widely: "yes" approaches a majority in Scotland (47% to 49% in summer 2026), but remains firmly in the minority in Wales (26%) and Northern Ireland (35.8% for reunification).
- Despite an unprecedented political signal in response to the costs of Brexit, the UK government's refusal and the length of accession processes make effective integration unlikely before the mid-2030s.

On 23 June 2016, 51.9 % of British voters opted to leave the European Union. But behind this national majority lay a deep territorial divide : in Scotland, 62 % of voters wished to remain in the EU, as did 55.8 % in Northern Ireland.1 Ten years later, questions about their constitutional future are back at the forefront : polls conducted between late May and August 2026 put support for Scottish independence at between 47 and 49 %, ahead of opposition (43 to 45 %), while support for independence in Wales (26 % in January 2026) and Irish unity in Northern Ireland (35.8 % in May 2026) remains firmly in the minority.234 On 14 September 2026, in Cardiff, the leaders of the Scottish National Party (SNP), Plaid Cymru and Sinn Féin signed a joint memorandum calling for closer cooperation and for constitutional change to be facilitated in their respective territories. They also affirmed their desire to restore and strengthen ties with Europe, envisaging a future within the European Union.5

This initiative raises a fundamental question : could Brexit, which was intended to redefine the United Kingdom’s relationship with Europe, ultimately contribute to its own fragmentation and pave the way for new EU accessions, thereby changing the Union’s boundaries ?

Between independence movements, the right to self-determination and legal obstacles, such a development would transform the United Kingdom’s political balance, as well as the Union’s institutional and economic prospects. The argument advanced here is that the memorandum sends a strong political signal, but the legal and European pathways available to the three nations differ too greatly to speak of a common front for EU accession.

To understand the stakes of this potential realignment, we must first revisit the historical trajectories of Scotland, Wales and Northern Ireland, as well as the consequences of Brexit for each of these territories (I). We must then examine the ambitions and demands set out in the joint memorandum (II), before analysing the conditions for possible accession to the European Union and the implications for the EU (III).

### I. Three national trajectories in the wake of Brexit

The United Kingdom, formed gradually through several unions, brings together four nations with distinct historical identities and constitutional aspirations. Although Brexit has reignited tensions between London and the devolved governments, these tensions have much deeper historical roots. Devolution, introduced in the late 1990s, gave Scotland, Wales and Northern Ireland their own parliaments or assemblies and governments. However, constitutional matters, beginning with the union between the nations, remain reserved to Westminster, a fact that shapes the entire analysis that follows.67

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#### A. Scotland at the heart of a contested union

Independent for several centuries, the Kingdom of Scotland united with England in 1707 under the Acts of Union, which merged the two parliaments to form the Kingdom of Great Britain while preserving certain distinct institutions, notably its legal system, church and education system. Scottish national identity remains central to political debate today. At the 2014 independence referendum, however, 55.3 % of voters chose to remain in the United Kingdom, on a turnout of 84.6 %.8 Two years later, Scots voted to remain in the European Union by a margin of 24 percentage points.1 This divergence strengthened the SNP’s argument that independence would allow Scotland to regain its place within the EU.

The current balance of power is more favourable to independence supporters than it was in 2014, although they do not command a parliamentary majority on their own. At the May 2026 election, the SNP won 58 of the 129 seats, six fewer than in 2021, on a turnout of 53.2 %. Together with the 15 Green MSPs, however, pro-independence parties once again hold a majority, with 73 seats.9

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A legal obstacle nevertheless remains : in 2022, the UK Supreme Court ruled in the case of *Reference by the Lord Advocate*, on 23 November, that the Scottish Parliament could not unilaterally hold another independence referendum.6 As for public opinion, polling in 2026 varies by pollster : YouGov and Ipsos still put the “No” vote ahead in the spring, whereas Survation, Find Out Now and Norstat put “Yes” at between 47 and 49 % in the summer, equivalent to approximately 52 % against 48 % once undecided voters are excluded.2

[Graphique interactif — voir la page web]

#### B. Wales: from a quest for autonomy to independence

Gradually incorporated into the Kingdom of England in the sixteenth century through the Acts of Union of 1535 and 1542, Wales has a strong cultural and linguistic identity. Its political autonomy developed later : in 1997, the Welsh narrowly approved the creation of a devolved assembly, with 50.3 % of the vote and turnout of around 50 %.10 Unlike Scotland, Wales voted for Brexit in 2016, with 52.5 % backing Leave and 47.5 % voting to remain.1 This result does not, however, mean that the Welsh reject all forms of European cooperation, although no recent poll measures support for an independent Wales joining the EU. Debates over agricultural funding, regional development and economic relations with the EU continue to inform discussions about the country’s future. Plaid Cymru, the Welsh nationalist party, now advocates independence and closer ties with Europe.

The Welsh scenario should not be equated with the Scottish one, as support for independence remains a minority position : 26 % against 54 % in a YouGov poll in January 2026, and 35 % against 50 % in a Redfield and Wilton poll in March 2025.3 Nevertheless, the 7 May 2026 Senedd election put Plaid Cymru in first place for the first time, with 43 of 96 seats (35.4 % of the vote), ahead of Reform UK (34 seats). Rhun ap Iorwerth leads a minority government and has ruled out an independence referendum during his first term, while retaining the goal as a long-term objective.11

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#### C. Northern Ireland: between British identity and the prospect of a united Ireland

Created in 1921 when the island of Ireland was partitioned, Northern Ireland remains deeply shaped by the coexistence of communities with different constitutional aspirations : unionists wish to maintain the link with the United Kingdom, while Irish nationalists support reunification of the island. This two-camp picture is an oversimplification, however, as the unionist camp includes the DUP, UUP and TUV, while part of the electorate identifies as neither unionist nor nationalist, as reflected in support for the Alliance Party.4 The 1998 Good Friday Agreement laid the foundations for the peace process and enshrined the principle of consent in any change to the territory’s constitutional status. In 2016, 55.8 % of Northern Irish voters chose to remain in the EU.1 Brexit subsequently complicated trade relations between Great Britain, Northern Ireland and the Republic of Ireland, an EU member state. The Windsor Framework (2023) sought to ease these difficulties while preserving the absence of a physical border on the island.

Sinn Féin came first in the 2022 Northern Ireland Assembly election, winning 27 of 90 seats, a first for an Irish nationalist party, and its vice-president Michelle O’Neill has been First Minister since February 2024.12 Public opinion, however, has not followed suit : a survey by the Institute of Irish Studies at the University of Liverpool, conducted in May 2026, put support for Irish unity at 35.8 %, its lowest level in ten years, down from 40.6 % in 2025.4 In this context, Sinn Féin advocates reunification with the Republic of Ireland, a goal distinct from the Scottish and Welsh projects and one that raises a fundamentally different European question.

Thus, while these three nations now share certain demands concerning self-determination, their trajectories and objectives remain distinct. Brexit has made these differences more visible, but it has not demonstrated that a majority of their inhabitants now wish to leave the United Kingdom : Scotland alone comes close, as the table below shows. The next section therefore examines the memorandum signed in Cardiff, its content and its limitations.

| Nation | 2016 vote to remain in the EU | Current support for constitutional change |
| --- | --- | --- |
| Scotland | 62.0 % | 47 % for independence against 43 % (Survation, August 2026) |
| Wales | 47.5 % | 26 % for independence against 54 % (YouGov, January 2026) |
| Northern Ireland | 55.8 % | 35.8 % for Irish unity (University of Liverpool, May 2026) |

The questions asked differ from one nation to another, so this comparison provides an indication of the scale of support rather than an exact measurement.

### II. Political rapprochement without a shared project

The three parties took a further step in their cooperation by signing a Memorandum of Understanding in Cardiff on 14 September 2026. The signatories were John Swinney, leader of the SNP and Scotland’s First Minister; Rhun ap Iorwerth, leader of Plaid Cymru and Wales’s First Minister; and Michelle O’Neill, vice-president of Sinn Féin and Northern Ireland’s First Minister. They signed in their capacity as party leaders, not in their government roles.5 The SNP and Plaid Cymru have long cooperated at Westminster, where Sinn Féin does not take its seats because of its abstentionist policy. The novelty, therefore, lies in bringing all three parties together in a single document. Their aim is to coordinate efforts to secure constitutional change in their respective territories and defend their populations’ right to determine their future. The text explicitly calls on the British government to “prepare for, plan and facilitate constitutional change” (author’s translation of the quotation reported by ITV News).5

This rapprochement rests on a shared assessment by the signatories : Brexit has weakened their economies and reduced opportunities for their populations. This is the parties’ own diagnosis, but it is supported by estimates from the Office for Budget Responsibility, which judges that the Trade and Cooperation Agreement will reduce UK productivity by 4 % in the long term and trade by around 15 % compared with EU membership.13 The economic cost of Brexit is analysed in greater detail in the PromethEUs article [Why the United Kingdom should rejoin the EU](https://prometheus-euro.eu/en/news/why-the-united-kingdom-should-rejoin-the-eu). The memorandum therefore seeks to strengthen cooperation in three main areas : economic development and tackling inequality, the exploitation of renewable energy resources, and European and international relations. Energy cooperation would focus primarily on offshore wind in the North Sea, Irish Sea and Celtic Sea. It appears feasible in terms of investment, research and supply chains, but remains constrained by the fact that energy regulation largely falls under Westminster’s authority.

The memorandum’s central point lies in the nature of this coordination. Despite their willingness to cooperate, the document explicitly acknowledges that the parties advocate distinct constitutional projects. The SNP seeks Scottish independence, Plaid Cymru seeks Welsh independence, while Sinn Féin advocates Irish reunification, which would entail Northern Ireland joining the Republic of Ireland, already an EU member. The memorandum sets neither a common timetable nor a uniform procedure : each nation must be able to determine its future “in its own way and in its own time”.5

This distinction is fundamental, because the legal obstacles differ. In Scotland, the obstacle is the 2022 ruling mentioned above. In Wales, a referendum would also require an appropriate legal basis and action by UK institutions : the Wales Act 2017 lists “the union of the nations of England and Wales” among reserved matters. An enabling act passed at Westminster would therefore be necessary, as it was before the 2014 Scottish referendum, and no court has ruled on the issue.7 In Northern Ireland, the Good Friday Agreement provides a democratic route to reunification, allowing for a referendum on Irish unity when the conditions set out in the agreement are met. The Secretary of State for Northern Ireland must call such a referendum if it appears likely to him or her that a majority of voters would wish Northern Ireland to cease to be part of the United Kingdom and form part of a united Ireland. A new referendum cannot be held within seven years of the previous one.14 On the Irish side, Articles 2 and 3 of the Constitution make a united Ireland contingent on the consent of a majority in both jurisdictions on the island, requiring parallel votes in the North and South.15

| Nation | Legal obstacle or mechanism | Decision-making authority |
| --- | --- | --- |
| Scotland | Power reserved to the UK Parliament: Supreme Court ruling of 23 November 2022 | UK Parliament (Westminster) |
| Wales | The union of the nations of Wales and England is a reserved matter (Wales Act 2017); no court ruling on the issue | UK Parliament, through enabling legislation |
| Northern Ireland | Mechanism provided for by the Good Friday Agreement and the Northern Ireland Act 1998 (Schedule 1) | Secretary of State for Northern Ireland, with a parallel vote in the Republic of Ireland |

The memorandum is an instrument of political cooperation and pressure. It declares no independence and initiates no process of secession. Its significance lies in the stated intention to coordinate movements that have until now followed distinct paths and to place the constitutional question at the heart of British debate. The initial reactions confirm this political reading. According to ITV News, Downing Street has indicated that Prime Minister Andy Burnham is committed to the Union and will not support new referendums. A letter to John Swinney keeps a Scottish referendum “off limits”, although Mr Burnham told the House of Commons that a new vote could be possible if there were a “clear consensus” in Scotland. Northern Ireland’s Deputy First Minister Emma Little-Pengelly (DUP), for her part, accused Michelle O’Neill of using her office as First Minister for political purposes.165 The reports available do not, at this stage, mention any reaction from the Irish government or the European institutions.

Beyond challenging the United Kingdom’s territorial organisation, the text presents Europe as a shared political horizon : the signatories state that “the future of our nations belongs in the European Union”.5 But a political desire to join the EU is not the same as an official application, much less a guarantee of accession. Only a state can apply under Article 49 of the Treaty on European Union : neither Scotland nor Wales can do so while remaining part of the United Kingdom.17

Any eventual independence or reunification would therefore usher in a period of complex negotiations, covering in particular the new states’ international status, their relations with the United Kingdom and their future relationship with the Union. In practical terms, this would involve the division of debt and assets, currency, the border with England, the Common Travel Area with Ireland, the UK’s nuclear deterrent based in Scotland and NATO membership. The EU-27 would have to decide whether to accept new members and under what conditions.

The Cardiff memorandum thus marks an important political milestone without prejudging the outcome. It turns national demands into a more structured cooperation project and revives a question that extends far beyond the United Kingdom’s borders. The implications for the Union remain to be examined.

### III. Accession and implications for the European Union

#### A. Accession is possible, but far from automatic

An independent Scotland or sovereign Wales would not automatically retain the membership status enjoyed by the United Kingdom. In 2012, Commission President José Manuel Barroso wrote that a newly independent state would, by virtue of its independence, become a third country vis-à-vis the Union. A Commission spokesperson confirmed this position in March 2017.18 Each would, in principle, have to follow the procedure set out in Article 49 of the Treaty on European Union : submitting an application, negotiating the adoption of the EU acquis, obtaining the unanimous approval of the member states, and having the accession treaty ratified by each of them in accordance with their constitutional requirements. This makes the process longer and more uncertain than negotiations alone might suggest.19 There is no direct precedent for a state emerging from the secession of an EU member state, leaving the Union without an established doctrine for such a case.

A candidate would also have to meet the Copenhagen criteria, which require stable institutions, a functioning market economy and the capacity to assume the obligations of membership, including adherence to the objectives of political, economic and monetary union.20 For Scotland, these criteria are central to the current debate, particularly the public deficit and currency. According to the GERS 2025–26 report, Scotland’s notional deficit stands at 10.9 % of GDP, compared with 4.2 % for the United Kingdom, while the treaties set a reference value of 3 % for the public deficit.21 New member states are in principle committed to adopting the euro once they meet the relevant conditions, which would raise the question of currency choice. The Schengen issue would also come up against the Common Travel Area with Ireland.

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The timetable would ultimately depend on the willingness of each capital. Unanimity gives every member state a veto, and countries facing internal territorial claims, with Spain often cited as an example, would scrutinise the precedent closely. The length of such a process can be gauged from Croatia, which applied in 2003 and joined in 2013, while several Western Balkan candidates have been waiting for more than fifteen years.

The Northern Irish scenario would be different : reunification with the Republic of Ireland would raise a distinct legal question, linked to the Good Friday Agreement and the island’s European status. At the summit of 29 April 2017, the EU-27 had a declaration entered in the European Council minutes recognising that an agreed mechanism could lead to a united Ireland through peaceful and democratic means, and that “the entire territory of such a united Ireland would thus be part of the European Union”.22 This declaration, distinct from the negotiating guidelines adopted on the same day,23 expresses a political position of the EU-27 rather than a treaty provision, and indicates the direction a negotiation would most likely take. The legal context supports this approach : Articles 2 and 3 of the Irish Constitution already refer to the entire island, and people in Northern Ireland can already obtain Irish, and therefore EU, citizenship.15 No third application for membership would be needed : the territory of the Union would extend across the entire island.

#### B. New representation within the European institutions

The arrival of new member states would alter the Union’s institutional balance. Scotland and Wales could represent their interests directly in the Council of the EU, take part in the work of the European Council and have representation in the European Parliament. They would also participate in the formation of the European Commission under the rules applicable to member states : currently, each member state has one Commissioner, one head of state or government on the European Council, and one judge at the Court of Justice.

The figures give an indication of the potential weight of these countries. Scotland has around 5.55 million inhabitants24 and Wales around 3.19 million.25 In the European Parliament’s 2024–2029 term, Ireland has 14 seats, Slovakia, Denmark and Finland have 15 each, and Croatia has 12. These are countries with populations comparable to Scotland’s, while Croatia has a larger population than Wales.26 As a rough estimate, Scotland could therefore expect around fifteen MEPs and Wales around ten. The two countries are considered together here, but their prospects differ markedly : with 47 to 49 % support for independence in recent polls, Scottish independence is a serious possibility, whereas Welsh independence, backed by 26 %, remains a distant prospect.

This development could enrich European debates, particularly on energy, maritime affairs, agriculture and regional policy, including North Sea fisheries, offshore wind, the common agricultural policy and cohesion policy. However, it would also require a reassessment of the allocation of parliamentary seats and decision-making balances. The treaties cap the European Parliament at 750 members, plus its President, and apply the principle of degressive proportionality, with a minimum of 6 and a maximum of 96 seats per member state.27 As the Parliament has had 720 members since 2024, there is room for around thirty additional seats, which would in principle be enough for Scotland and Wales but would require redistribution in the event of any further enlargement. New accessions would change the map of Europe and influence compromises among the EU-27.

#### C. Economic opportunities, but also trade challenges

Membership of the single market could facilitate trade in goods and services with other member states, strengthen scientific cooperation and provide access to European research and regional development programmes. In Scotland’s case, whose government officially advocates future accession, joining the single market as an independent state is presented in particular as a way to facilitate trade and attract investment. Scottish export figures illustrate the stakes : in 2023, exports reached £93.1 billion, of which around 59.5 % went to the rest of the United Kingdom and 18 % to the Union, excluding oil and gas.28 This balance is the argument most often advanced by opponents of independence. At this stage, neither the memorandum nor the reports consulted set out proposals on currency or the border.

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These potential benefits must nevertheless be put into perspective. An EU-member Scotland and the rest of the United Kingdom outside the Union would operate under different regulatory and customs frameworks. A customs and regulatory border could emerge between Scotland and England. The Windsor Framework and the Common Travel Area with Ireland show how a border between two regulatory regimes can be managed, but at the cost of specific controls and rules. Negotiations would also have to cover contributions to the EU budget, the application of single-market rules and the obligations associated with membership. Scotland would be a net contributor to or beneficiary of the EU budget depending on its national income and the amounts received under the common agricultural policy and cohesion policy, which would be subject to negotiation.

For the Union, the arrival of new members could strengthen its presence in the North Sea, its energy capacity, particularly offshore wind, its fisheries and port resources, and its diplomatic weight. Security considerations also change the strategic equation : the UK’s nuclear deterrent is based on the Clyde in Scotland, the SNP wants it removed, and NATO membership would become a subject of negotiation. Accession would also entail budgetary and institutional adjustments. The outcome would be favourable to the Union provided that a prior agreement settled debt, currency and border issues before accession ; without such an agreement, the Union would import a bilateral dispute into its own institutions.

### Conclusion

Brexit has opened a debate about the fragmentation of the United Kingdom, but it is not enough in itself to produce new accessions. It was intended to redefine the United Kingdom’s relationship with the European Union, yet its consequences continue to fuel debate over the constitutional future of its nations. The memorandum changes nothing in law, but it changes the debate : the rapprochement between the SNP, Plaid Cymru and Sinn Féin illustrates a desire for cooperation among movements that, despite their different objectives, are calling for greater control over their political future. Three conclusions emerge : the memorandum is a political signal, the legal pathways differ from one nation to another, and the implications for the Union depend above all on the Irish and Scottish cases.

Possible Scottish or Welsh independence, or Irish reunification, could have significant implications for the European Union, from its institutional representation to its trade relations. These scenarios nevertheless remain subject to considerable political and legal obstacles, and no accession can be taken for granted. The Irish scenario is the most advanced legally, since a mechanism for consultation exists and the EU-27 have already indicated that the island would remain within the Union, although support at 35.8 % makes the outcome uncertain. The Scottish scenario is the most uncertain because it depends on an agreement with Westminster and clear answers on debt, currency and the border. The Welsh scenario is the most remote. No referendum is scheduled and Downing Street has ruled one out ; given that Croatia’s accession took ten years, actual membership before the mid-2030s appears unlikely.

The question therefore goes beyond the United Kingdom’s future alone : to what extent is the European Union prepared to welcome new states while preserving its cohesion and decision-making capacity ? At a time when enlargement is returning to the centre of European debate, this possibility invites reflection on the Union’s future borders and on the tension between the unanimity required for accession and the speed that a British political timetable might demand.

The Union should therefore clarify in advance its position on the accession of a territory emerging from a member state, for example through a European Council declaration specifying the applicable criteria, the role of a separation agreement with the United Kingdom and the territory’s status during the transition, so that it does not have to improvise when the situation arises.

For an analysis of the economic cost of Brexit, which underpins the three parties’ European argument, we invite you to read or revisit our article:

[![](https://prometheus-euro.eu/assets/uploads/cover_20260727204756_0411874ae992fa64.jpg)À lire aussiWhy the United Kingdom should rejoin the EUTen years after the fateful referendum of June 2016, the debate over the United Kingdom's European future is no longer a matter of mere speculation among theorists. As the structural costs of Brexi…](https://prometheus-euro.eu/en/news/why-the-united-kingdom-should-rejoin-the-eu)

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Cite as: Lilà Schwartz, "Brexit: What if the United Kingdom accelerated its own break-up… to Europe’s benefit?", PromethEUs, 2026-10-26, https://prometheus-euro.eu/en/news/brexit-what-if-the-united-kingdom-accelerated-its-own-break-up-to-europe-s-benefit