The UK Supreme Court has, since its creation in 2009, taken on a more visible role in checking the use of executive power than the senior courts that came before it. In Miller 1 (2017) it ruled that the Brexit Article 50 notification required an Act of Parliament rather than a use of the royal prerogative. In Miller 2 (2019) it held that Boris Johnson's prorogation of Parliament had been unlawful because it frustrated the constitutional functions of the legislature. Defenders of the Court argue that these rulings simply defended Parliament against unlawful uses of prerogative power, and that policing the legality of executive action is exactly what a Supreme Court is for in a parliamentary democracy.

However, the Court is also visibly reluctant to override government decisions on grounds of policy rather than legality. In Begum (2021) the Court deferred to the executive on national security and declined to second-guess the Home Secretary's decision. In the Rwanda case (2023) the Court found the policy unlawful on legal grounds, but Parliament responded by passing the Safety of Rwanda (Asylum and Immigration) Act 2024, declaring Rwanda safe by statute and overriding the judicial finding. The Court accepted that result without resistance. Section 35 orders, used for the first time in 2023 over the Scottish Gender Recognition Reform Bill, have given the UK government a parallel statutory route to block devolved legislation that the Court has not challenged.

This pattern suggests a more careful judiciary than the headlines imply. The Court has policed prerogative power vigorously when constitutional fundamentals were at stake, but has been quick to defer to Parliament once primary legislation enters the picture. Critics argue this is exactly the right balance for an uncodified constitution in which Parliament remains sovereign. Others reply that the Court has nonetheless become a political actor in everything but name, because every major ruling it issues is now read for its political consequences as much as its legal reasoning.

Devolution was introduced under the Blair government from 1997, after referendums in Scotland (74 per cent Yes), Wales (50.3 per cent Yes), and Northern Ireland via the Good Friday Agreement of 1998. The original political case was that handing meaningful policy autonomy to the nations would settle nationalist demand for full independence by giving voters self-government within the Union. On the headline test, that case still holds. The 2014 Scottish independence referendum returned a 55 per cent to 45 per cent vote to remain in the United Kingdom, and the Northern Ireland Assembly has prevented a return to the violence of the Troubles even when it has been suspended, most recently from 2022 to 2024 over the Northern Ireland Protocol.

However, devolution has also produced an asymmetric settlement in which each nation has different powers and each has acquired political institutions that can challenge Westminster. Scotland varies income tax under the Scotland Act 2016 and runs free university tuition. Wales has used the Senedd as a policy laboratory, including the default 20mph speed limit. The use of a Section 35 order in 2023 to block the Scottish Gender Recognition Reform Bill, the first such use, showed how quickly devolved disputes can become Union-level constitutional crises. The Sewel Convention, by which Westminster will not normally legislate in devolved areas without consent, has been overridden in practice on Brexit-related legislation and is not enforceable in the courts.

This leaves a settlement that is widely described as quasi-federal but constitutionally uncertain. Supporters argue that asymmetric devolution has flexed to absorb new demands without breaking up the Union, and that the absence of an English parliament is a tolerable feature of an unwritten constitution. Critics reply that the settlement is provisional and that the rise of any UK government perceived as hostile to devolved interests, particularly in Scotland, could produce a renewed and successful independence movement. The Union is still standing, but the question is whether devolution has saved it or merely deferred the choice.