Ten years after the Brexit referendum: A more fragile union

When Scotland’s then first minister, Nicola Sturgeon, called for a second referendum on Scottish independence in March 2017, she claimed that Brexit was “a significant and material change in the circumstances that prevailed in 2014.” The Scots had voted by a margin of 62 per cent to remain in the EU. They should now be offered a choice: stay in a post-Brexit UK or seek independence with the possibility of rejoining the EU. 

In those uncertain times, it seemed possible that Brexit would not only shake the EU but rock the foundations of the UK as well. Northern Ireland had also voted to remain, and the Irish border was emerging as a major obstacle to a smooth departure. Although Wales had voted to leave, its then first minister Carwyn Jones shared Sturgeon’s frustration at the UK government’s refusal to involve devolved administrations meaningfully in the Brexit negotiations – and to contemplate a softer Brexit that would have kept the UK in the single market. 

Yet the feared disintegration of the union did not materialise. The UK government simply refused to agree to a second Scottish independence referendum. “Now is not the time,” said Theresa May. Nor did Edinburgh and Cardiff secure a meaningful role in the negotiations with the EU. Westminster pressed ahead with various pieces of Brexit-related legislation despite the refusal of consent by both devolved legislatures. The Sewel convention, recognised in statute, states that UK Parliament will “not normally” legislate on devolved matters without their agreement – and Brexit exposed its limits. To add insult to injury, the Internal Market Act of 2020 deepened the resentment by imposing a version of the UK internal market which was widely seen by the devolved governments as constraining their regulatory powers. 

Northern Ireland, the only part of the UK that shared a land border with the EU, meanwhile became a pawn in the struggle of competing visions of Brexit. Supporters of a softer departure were willing to accept closer legislative alignment with the EU to preserve an open border on the island of Ireland. Hard Brexiters insisted on leaving the single market and customs union while rejecting new barriers in the Irish Sea. Those demands were difficult to reconcile.  

“Brexit has produced a paradox. It made the union more politically fragile, but separation more complicated.” 

The Irish border conundrum was used to defeat Theresa May’s deal and ultimately bring down her government. Boris Johnson broke the impasse by casually accepting a border down the Irish Sea as the price of a negotiated exit. The Windsor Framework, later agreed by Rishi Sunak’s government, eased some of the practical consequences but did not alter the underlying reality: Northern Ireland now has a different trade relationship with the EU than the rest of the UK, adding to the grievances of the unionist community.  

Brexit has therefore produced a paradox. It has made the union more politically fragile, but separation more complicated. An independent Scotland or Wales would face a stark choice: rejoin the EU and its single market, or negotiate continued participation within the UK internal market. Unless the rest of the UK was itself seeking to re-enter the single market, it would be difficult to do both. For Northern Ireland, reunification would make the Irish Sea barriers more consequential, potentially undoing the benefits that have allowed claims that businesses there have the “best of both worlds”. 

The union has survived the Brexit storm, and leaving the UK is now more complicated than it once was. Brexit may have been imposed on an unwilling Scotland and Northern Ireland. But was that a risk worth taking? For some, perhaps it was. Yet something has been broken in the process. For much of the period since the Union of 1707, an unspoken tenet of the British polity was that the centre did not impose its will on a reluctant Scotland. The ambiguity that underscored that reticence – over whether sovereignty rested with the Scottish people or the UK Parliament – has been swept aside. 

Brexit also revealed an ignorance at the metropolitan centre of the fragile and complex conditions of Northern Irish politics and, at times, a cynical willingness to exploit the border question for ends other than the well-being of the people of Northern Ireland. While the immediate crisis has been resolved, the damage to trust will be harder to repair. 

For the first time, nationalist parties now lead the governments of all three devolved parts of the UK. Close to half of Scots still support independence, while the Welsh nationalist party Plaid Cymru won the most seats in the May 2026 Senedd elections.  

A decade after the Brexit referendum, the stability of the UK is more contingent than ever on circumstance. And circumstance may yet bring another turn of the wheel. A future UK government committed to leaving the European Court of Human Rights could place further strain on the Brexit settlement, including the Trade and Co-operation Agreement, which governs nearly half of the country’s trade. It could also unsettle the Good Friday/Belfast Agreement, which underpins peace and governance in Northern Ireland. How might voters in the devolved nations respond? Brexit has not undone the union. But the strain it placed on the ties that hold it together has not yet run its course. 

Philip Rycroft was permanent secretary at the Department for Exiting the EU (2017-19) and second permanent secretary at the Cabinet Office (2015-17).  

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