Six years after Britain formally left the European Union, the argument over Brexit is acquiring a new and rather unexpected dimension.It is no longer confined to the familiar question of whether Britain itself should seek a closer relationship with Europe. The constitutional future of the United Kingdom is now becoming entangled with the question of Europe — and Scotland, Wales and Northern Ireland are increasingly making the connection explicit.This week, the leaders of the Scottish National Party, Plaid Cymru and Sinn Féin, met in Cardiff and signed an agreement asserting the right of their nations to determine their own constitutional futures. The memorandum declared that “each of our nations has the right to determine its own future, through democratic means and in accordance with the wishes of its people”. It called on the British government to “prepare for, plan and facilitate constitutional change” in Scotland, Wales and Northern Ireland. It also declared: “We believe the future of our nations belongs in the European Union.”It was an extraordinary piece of political theatre. For the first time, the governments in Edinburgh, Cardiff and Belfast are led by parties committed to leaving the UK, although the leaders met in Cardiff as party leaders rather than formally representing their governments.John Swinney, Scotland’s First Minister and SNP leader, is pressing for another independence referendum. Sinn Féin’s Michelle O’Neill is campaigning for the possibility of a referendum on Irish reunification. Plaid Cymru’s Rhun ap Iorwerth has been more cautious about timing, ruling out a Welsh independence referendum for the time being while seeking greater powers for Wales.The EU, therefore, sits at the heart of an argument that was once largely about Westminster and the nations of Britain. That is where the wider British debate becomes interesting.The UK government is not proposing to reverse Brexit. Indeed, the language from London remains that Britain is outside the EU and will remain so. But the practical relationship is changing.The UK and EU have been negotiating a substantial reset involving food and agricultural trade, emissions trading, electricity, youth mobility, education and security. Britain has also agreed to work towards association with a new youth experience scheme.On security, the two sides have established a Security and Defence Partnership covering such areas as support for Ukraine, defence industry cooperation, military mobility, space security and resilience against hybrid threats. The British government described it as establishing “a new era of security co-operation between the UK and EU”.Rachel Reeves, the former Chancellor of the Exchequer, has gone further in her public language, arguing that Britain should move towards a “trusted economic and security partnership” with the EU in which “the default is that the UK is included not excluded”.So, Britain is not rejoining Europe. But it is, step by step, attempting to make Brexit work with fewer of the frictions that have emerged since departure.The paradox is that this closer relationship with Europe is happening at precisely the moment when the constitutional unity of Britain is under renewed pressure.For Scotland, the argument is particularly straightforward. The country voted by 62 per cent to remain in the EU in the 2016 referendum, while the UK as a whole voted to leave. Scotland subsequently left the EU despite that vote.Swinney now argues that Scotland should have another opportunity to decide whether to become independent. The SNP points to the pro-independence majority among MSPs returned at the latest Scottish election as evidence of a mandate, while Westminster has so far resisted granting the legal authority for another referendum.For Wales, the politics are different. Welsh voters also voted to leave the EU in 2016. Plaid Cymru nevertheless now argues that Brexit has damaged Wales and that the country’s future should ultimately be decided by the Welsh people.Northern Ireland presents an altogether different constitutional problem. Under the Good Friday Agreement, a referendum on Northern Ireland’s constitutional status can be called when the relevant conditions are judged to exist. Sinn Féin argues that preparations for such a vote should begin. The issue has also received fresh international attention following Donald Trump’s recent remarks about Irish reunification.For India, this is not an abstract British constitutional argument. New Delhi has traditionally dealt with Britain as a single sovereign state. Yet the economic and institutional links with its constituent nations have become increasingly substantial.Scotland is an obvious example.The Indian Consulate in Edinburgh describes India-Scotland relations as deepening across trade, investment, education, renewable energy, technology, life sciences and culture. Indian companies have a substantial presence in Scotland, while Scottish institutions have built extensive relationships with India.Swinney himself has long been engaged with India. During a 2018 trade mission to India, he helped develop commercial and educational links, while in September 2025 he met India’s then High Commissioner Vikram Doraiswami to discuss strengthening India–Scotland cooperation. The Indian Consulate said the two discussed “trade, investment, education, culture and innovation”.That does not mean India should take a position on the constitutional future of Britain. Far from it. New Delhi has every reason to deal with whichever institutions have democratic authority, while maintaining its longstanding relationship with the UK government.But Indian policymakers and businesses will have to watch the evolving British settlement carefully.The reason is simple. Brexit was presented as a restoration of sovereignty to Westminster. The emerging reality may be rather more complicated: Westminster is simultaneously negotiating a closer practical relationship with Brussels while the devolved nations are demanding greater autonomy from Westminster and even a possible future outside the UK.The result could be a Britain whose relationship with Europe is gradually being reconstructedAnd that raises the question at the heart of the current debate: was Brexit the conclusion of Britain’s European argument, or merely the beginning of a much longer renegotiation—both between Britain and Europe and between Westminster and the nations within the UK?