The visitor to Derby’s city museum, perhaps attracted there by its Joseph Wright paintings, will also discover a recreated 17th-century, oak-panelled living room. The room is on display because it was in Derby, in December 1745, that Prince Charles Edward Stuart called off his Jacobite army’s advance on London and began the retreat to Scotland. It was a turning point for the British monarchy and for the union. Four months later, the prince’s forces were brutally routed at Culloden. In the 277 years since then, no one else emerged from Scotland to challenge the British political order as fiercely as the Bonnie Prince – until Nicola Sturgeon. True, Sturgeon never invaded England. But then she never needed to. From Hanoverian Edinburgh, underpinned by successive nationalist election victories, she has rocked the assumptions underpinning the union of Scotland and England more effectively than anyone in modern British history. Sturgeon’s resignation in February probably caused almost as much celebration in today’s London political circles as the prince’s retreat from Derby. Back then, church bells were rung, bonfires lit and drunken mobs attacked houses thought to contain Jacobite sympathisers. In the 21st century, by contrast, the political class kept its glee under wraps. Public tributes to Sturgeon have been mostly respectful. Congratulations to her successor, Humza Yousaf, this week have been courteous. Do not, though, be deceived. Most politicians from the UK-wide parties are cock-a-hoop about what is happening to the SNP. It is understandable that reaction, both in Edinburgh and London, to the changing of the nationalist guard has focused on the likely immediate consequences. The leadership election, in which Yousaf defeated Kate Forbes by 52%-48%, has exposed deep fissures that Sturgeon’s charismatic and disciplined style had kept hidden. And, with a super-important and potentially close UK general election due next year, in which Scotland’s Westminster seats could be critical, the changes in the SNP are pregnant with wider consequences. Few of these look encouraging for nationalists. Sturgeon resigned, it should be remembered, not because of her record of achievement, but because her political strategy on issues from independence to gender recognition was falling apart. Her approach was reliant on her own performative skills and on the party biting its tongue and mumbling about Scotland’s multiple internal problems in order to keep the focus on independence. It had run out of road. The roots of the difficult months that lie ahead for Yousaf all rest firmly in soil of the Sturgeon era. The six-week leadership election contest provided no solutions; instead, it has made the problems worse. Yousaf is a product, not a critic, of the cliquish top-down centralism that marked Sturgeon’s rule. The embarrassing decline in the party’s membership (and the many remaining members who did not vote in the election) speaks to a faltering party, not a surging one. The attempt to conceal the facts, and the investigation into the financial role of Peter Murrell, Sturgeon’s husband and former SNP chief executive, are unfinished and extremely troublesome business. Some of this is hardly surprising, perhaps, given the party has been in charge for so long. All governments succumb to political entropy eventually. Yet this provides Yousaf with a dauntingly difficult inheritance that he will struggle to master. If Forbes had won the leadership, the internal divisions might have come to a head even sooner. Even so, and given his former responsibility for the Scottish NHS, Yousaf will do improbably well to persuade Scots that he is not part of the problem. The net effect, in the short term, is that the SNP’s command of Scottish politics looks more vulnerable. Support for independence is down. So is satisfaction with the government. The SNP’s lead over Labour has shortened. Yousaf is less popular than Sturgeon. The SNP needs a high-profile early electoral test like a hole in the head right now. But just such a test may come in the Labour target seat of Rutherglen and Hamilton West, after the Commons standards committee’s recommendation to suspend the MP Margaret Ferrier for 30 days. All of this has naturally energised the SNP’s rivals. They see a transformed, post-Sturgeon Scottish political landscape in which SNP seats are ripe for capture and SNP hegemony tottering. Keir Starmer has become a regular visitor to Scotland. Rishi Sunak likewise. Confirmation from the Glasgow-based polling guru Sir John Curtice that Labour could take 10 of Scotland’s expected 57 seats in 2024 has been widely repeated. Yet while these immediate consequences unquestionably matter, some of the responses are surely getting ahead of the facts. The SNP – not Labour – is still Scotland’s most popular party. The SNP is still likely, on current projections, to win the majority of Scottish seats in 2024. Independence remains the choice of a very large minority of Scots and is particularly supported by younger Scots. If Sunak not Starmer wins in 2024, talk about the SNP’s eclipse may evaporate very fast. That is part, but only part, of the reason why it is important to think more carefully – and more historically – about the SNP, and the pressure for independence. These things are not going to disappear. There is no reason in modern Britain why they should. Indeed, there is every reason why they should not, especially when it has proved so hard to make an emotional case for the union. In his superbly stimulating new book, Untied Kingdom, on the imperial context of the slow breakup of Britain, Stuart Ward puts it this way: “Being British was always something of a stretch … Even at peak efficiency, to be British was heavily modulated by local inflections and a tangle of conflicting priorities. At no time during its roughly 300 years of popular currency did it provide watertight categories of inclusion or resonate uniformly from one constituency to the next.” Who of us can seriously claim, especially after Brexit, that to be British in 2023 is to have a share in an idea that is running at peak efficiency, or is likely to do so in the foreseeable future? The disruption of Britain, and its union, predates Brexit. It will also outlast it. Perhaps the greatest consequence of the 1745 rising was the idea of Scotland it bequeathed to later generations. Sturgeon’s goals were utterly different and were honed in a different era. But they too may endure. As Ward said to me this week: “For nationalism, this is a speed bump, not a car crash.” Martin Kettle is a Guardian columnist