In removing Britain from one union, one of Theresa May’s most difficult tasks will be ensuring she does not inadvertently contribute to the break-up of another.
Last month’s vote has emboldened nationalists in Scotland, Wales and Northern Ireland, many of whom argue that leaving the EU should prompt a re-examination of the future of the UK. But in reality, experts say, the devolved administrations have almost no legal power to stop Britain leaving the EU.
“Formally, the nations of the UK don’t have any power to in effect override Westminster sovereignty,” said Robert Hazell, professor of government and the constitution at University College London.
The devolution acts for Scotland, Wales and Northern Ireland all allowed Westminster to set foreign policy. This meant David Cameron, the former prime minister, could renegotiate Britain’s membership of the EU without having to secure the agreement of Edinburgh, Cardiff or Belfast.
There is one constitutional route for the devolved administrations to stall Brexit. They could argue that leaving the EU would alter the balance of powers between them and Westminster — something that by convention cannot be done without the support of both sides.
Westminster politicians could simply ignore that, arguing that these are exceptional circumstances, but this risks causing outrage. Michael Keating, chair in Scottish politics at Aberdeen university, said: “Westminster can get its own way, but to do so might violate that convention and so cause a serious [political] problem. Jim Gallagher, visiting professor of government at Glasgow university, argues that if nothing else, the devolved administrations can use their access to Whitehall to make sure they get power over issues previously decided by Brussels. “If you’ve not got the Common Agricultural Policy for example, then how are you going to set Scotland’s agricultural policy?” he said. “The administrations will say, ‘Devolve it to us’.”
However, the most significant power available to these administrations — especially in Scotland and Northern Ireland, where the majority voted against Brexit — is political rather than legal.
Mrs May knows that if she presses ahead with Brexit without the support of voters outside England, she could foment nationalist feeling further, possibly to the extent where the break-up of the UK becomes inevitable.
She acknowledged this after meeting Nicola Sturgeon, Scotland’s first minister, in Holyrood last week, after which she insisted she would take a “United Kingdom approach” to the Brexit talks.
This comment triggered suggestions that the Scottish government had been given a veto on Brexit, something Downing Street has been at pains to deny. “We are approaching this in a positive and constructive manner, but the final say of whether we leave the EU or not has already been taken by the British people,” said a spokeswoman this week.
The ultimate power held by Ms Sturgeon, as well as Plaid Cymru in Wales and Sinn Féin in Northern Ireland, is to push for a referendum on sovereignty.
It is in Northern Ireland where the stakes are highest. Membership of both the EU and the European Court of Human Rights underpins the Good Friday peace agreement, while EU funds worth €1.3bn since 1995 have helped pay for its implementation. Brexit also raises the prospect that there could be a physical border between the Republic of Ireland and Northern Ireland, along with passport checks and customs posts — something that could anger voters on both sides of the border.
Sinn Féin has already called for a referendum to unite Ireland in the wake of last month’s vote, but many in Westminster are concerned that such a prospect could reignite sectarian violence. James Brokenshire, the new Northern Ireland secretary, was quick to dismiss such a possibility last week.
The chance of a referendum is greatest in Scotland, where 62 per cent of voters were for Remain. Ms Sturgeon has said she thinks an independence referendum is “highly likely” in the wake of the Brexit vote, even suggesting it could happen next year.
However, her allies say privately that she does not want to call for a second independence vote unless she is sure of winning, which they say requires a sustained 60/40 lead in the polls. And while Brexit has given the independence cause a boost, its lead is only about 53/47 — not enough to give the Scottish National party the certainty it wants.
If the SNP wants to keep Scotland in the EU without another independence vote, it can push for membership even from within a country that is not a member. This kind of separate arrangement exists elsewhere, such as for Greenland, which is not an EU member, while its sovereign state of Denmark is.
Such a model would be unprecedented for a territory as big as Scotland, with 5m residents compared with Greenland’s 57,000, but it is beginning to pick up cross-party support. Ian Murray, Labour’s sole MP north of the border, said: “The government’s starting point should be to keep Scotland both within the EU and within the UK.
“It would be unprecedented, but right now everything is unprecedented — no member has ever left the EU before.”
In one key way, the interests of both the Westminster government and those outside England are aligned. Nobody in any of the administrations wants to move quickly with Brexit, believing that any delay strengthens their negotiating positions.
“One way to read Theresa May’s comments about a ‘United Kingdom approach’ is that it is actually part of her negotiation with Brussels,” said Mr Hazell. “She can delay triggering Article 50 if she argues that she needs to get the consent of the devolved governments first.”