It is sometimes claimed that a Brexit vote in June could lead to the break-up of Britain. Yet in politics, something of that break-up has already occurred. Politics in Northern Ireland has long followed its own path. But politics in the rest of Britain, which followed a reasonably unified set of rhythms and responses until the late 20th century, has now headed in a variety of very different directions. The devolved elections that are due in Scotland, Wales and Northern Ireland a week from now are likely to reflect that new diverse reality still further. We all need to get used to the fact. There is no such thing as British politics any more.

Next week’s Holyrood election marches very evidently to its own drum. In Scotland, the vote will above all be a verdict on the Scottish National party. The SNP has commanded Scottish politics for the last decade. Nicola Sturgeon, Scotland’s first minister, commands both the party and the country. The SNP has therefore framed the 2016 election as a vote about her. Its campaign slogan is “I’m with Nicola”. The cover of its manifesto consists of a picture of Ms Sturgeon and a single word: “Re-elect.” If all elections, as some have claimed, are a choice between “change” and “more of the same”, there is no room for doubt about which of these options the SNP is offering.

Few can doubt the outcome either. All recent polls show the SNP on course to increase their share of the poll from both 2011 and 2015. Instead, the main spectator interest in Scotland next week lies in whether Labour or the Conservatives will come second and in whether the Greens or the Liberal Democrats will come fourth. None of this will provide anything new to say about Labour’s chances of winning the UK general election in 2020 under Jeremy Corbyn – next week’s votes in England and Wales will be a more useful guide on that. Yet the SNP’s continuing ascendancy, while remarkable and not at all to be dismissed, is not without its problems.

By 2021, the SNP is likely to have ruled Scotland for 14 years. The perception of Scotland as effectively a one-party state is likely to grow. The manifesto contains no pledge to hold a second referendum before 2021 on independence, which is nevertheless now the great dividing line in Scottish politics, thus frustrating many radical activists. New tax powers, which Holyrood has already inherited and of which it will soon acquire more, mean it should become harder to blame all Scotland’s problems on London and the Conservatives, which may bring opposition parties (possibly new ones) into the frame. The 2016 campaign may not have dented the SNP’s hegemony, but the dominant issues on the stump have all been about tax and spending. That was true again at the Labour manifesto launch on Wednesday. The SNP has increasing vulnerabilities on these issues that are at present eclipsed by its enormous popularity.

Yet next week’s election to the 60-member Welsh assembly is altogether different again. Labour has come first in 36 out of 37 Wales-wide contests since 1918 and appears on course to make it 37 out of 38 next week. Nevertheless, Wales is changing. Ukip seems likely to gain assembly seats under the regional list top-up system next week. Plaid Cymru may mount a modest revival after a poor result last time. Yet in spite of the fact that Labour has always had a more nationalist stance in Wales than in Scotland, the party is in historic decline in Wales too. It may lose seats, though not on a Scottish scale. A Labour-led coalition or Labour minority government seems a likely outcome.

Yet this would not be a solid guide to politics in other parts of the UK either. Scottish politics, like those in Northern Ireland, now bear no relation to politics elsewhere. Welsh politics is neither a west British version of what is happening in England nor a minor key variation of the nationalist mood in Scotland. Even English politics is fractured, most obviously between London and elsewhere, but also in other ways. Post-industrial Britain is a disunited kingdom. And it increasingly has politics to match.