When the Scottish and Welsh parliaments were created on the eve of the millennium, the then Labour government in Westminster believed that it had engineered a win-win situation. Devolution, it was hoped, would see off any nationalist threat in Scotland and Wales. Meanwhile, the Labour party’s longstanding political dominance in both nations would see it take comfortable control of the two new parliaments.

That was then. Last week’s devolved elections left Scottish and Welsh Labour battered, bruised and humiliated. Plaid Cymru’s historic victory in Wales, and a fifth successive triumph for the Scottish National party (SNP), mean that pro-independence governments are now set for the first time to rule in Edinburgh, Cardiff and Belfast (where Sinn Féin won in 2022). The starting gun has been fired on a new and constitutionally contested era in the politics of the UK.

The seismic nature of Plaid’s win is hard to overstate. The Labour party’s grip on Welsh politics has been more or less absolute for more than a century. Yet last Thursday, the outgoing Labour first minister, Eluned Morgan, was among those to lose her seat.

Anger and disillusionment with Sir Keir Starmer’s unhappy premiership, and with Welsh Labour’s own failings in areas such as health and education, led progressive voters to migrate en masse to the nationalist alternative. A vote for Plaid was also seen as the best way to stop Nigel Farage’s Reform UK, which nevertheless will now form the official opposition in the Senedd.

In Scotland, Anas Sarwar’s pre-election gamble in calling for Sir Keir to resign failed as Scottish Labour recorded its worst result since devolution. Mr Sarwar hoped to distance his party from the sinking Westminster mother ship. But similarly to England, many progressives opted for the Scottish Greens, and Reform picked up voters in Labour’s post-industrial former heartlands. In a fragmented landscape, the SNP cruised home with its lowest share of the constituency vote share since 2007.

Concerted pressure for independence referendums is unlikely for now, although the prospect of a Farage‑led government in Westminster may shift the dial on that. Plaid’s leader, Rhun ap Iorwerth, has excluded the possibility of calling for a vote in the next Welsh parliament. Mr ap Iorwerth and the SNP leader, John Swinney, are both likely to lead minority administrations, though the buoyant Scottish Greens are pro-independence allies.

But a clean sweep for nationalist parties in the devolved nations will generate greater collaboration between them and a more combative climate in their relations with Whitehall. Sir Keir recently cautioned against being “overly deferential” to governments in Scotland and Wales, and ministers have used post-Brexit powers to bypass Holyrood and the Senedd. After this Labour meltdown for the ages, such a high-handed tone and approach is no longer sustainable.

The politics of Wales, in particular, is entering new territory. Mr ap Iorwerth will seek to demonstrate that by severing the umbilical cord with Labour, voters have empowered him to fight for a better deal on issues such as the control of Wales’s seabed and the funding of public transport. In an overcentralised state where London and its environs continue to hoover up resources and investment, that is a necessary battle to have. The fractious volatility of British politics indicates that the United Kingdom needs a new settlement. Last week’s results may help deliver one.

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