Thursday was a big day for Scottish Labour. Within minutes of the declaration that Labour had retaken Rutherglen and Hamilton West from the SNP, phones and social media lit up with triumphant messages from the winning party. And with good reason. This was the best result for Labour in a Scottish byelection since the second world war, and the worst for the SNP since the independence referendum upended Scottish politics. Some caveats apply. This was one of the SNP’s most marginal seats, where Labour prevailed as recently as 2017. A cloud of scandal hung over a contest triggered after the sitting MP Margaret Ferrier was sanctioned for repeatedly breaking Covid rules. As Boris Johnson has learned, voters judge such behaviour harshly. This was nonetheless a stunning result. The swing to Labour, at 20 points, was nearly double what would be expected from opinion polls which were already registering a substantial Scottish Labour advance. If such a swing were replicated across Scotland in a general election, Labour could gain 40 seats or more, all but wiping out the SNP. A decade of nationalist dominance would be swept away in a great red restoration. While such waves are not impossible in our volatile political times, they are not likely either. Thursday’s giant swing may instead reflect the appearance of a pattern familiar elsewhere: disgruntled voters registering their unhappiness with a weakened, scandal-tainted incumbent party. The SNP has run Scotland since 2007, and 2023 has been their most torrid year to date. Things may be different in a general election when Scottish eyes turn south to Westminster. But Labour doesn’t need a Scottish landslide. The smaller, but still substantial, advance registered in polling is already enough to bring 20 SNP seats or more into play. There were hints also in Rutherglen of something else which could boost Labour prospects in Scotland: anti-SNP tactical voting. The Conservative vote in the seat collapsed and the Liberal Democrat vote halved, as voters focused their attention on the top two contenders. Scottish Conservative voters, aware their party is out of the running locally and nationally, may be coming to see a tactical vote for Scottish Labour as a second-best option, a means to eject the SNP and show support for the union. Newly published polling research from the Tony Blair Institute suggests as many as one in six Scottish Conservatives may be willing to cast a tactical vote for Labour in SNP v Labour seats. For a decade, the SNP have profited from the fragmentation of the unionist vote in Scotland. That advantage may be waning. A return to electoral health in Scotland will have big implications for Labour in next year’s general election and beyond. Every seat taken from the SNP in Scotland is one gain less for the opposition to find in England and Wales. Gaining a dozen Scottish seats or more would substantially reduce the daunting swing Labour need to achieve a Commons majority. The SNP’s pummelling this week will also blunt one of the Conservatives’ favourite attack lines – that a weak Starmer government would be in the pocket of Scottish nationalists. Labour can credibly reply that they are running just as hard to defeat the SNP in Scotland as beat the Conservatives elsewhere. There will be no need to bargain with a rival on the ropes. Rutherglen could resonate beyond the general election as well. The return of a large cohort of Scottish Labour MPs would add a distinctive set of voices and interests to the Labour parliamentary party – politicians representing a devolved nation which has charted its own course in many policy areas and will remain a very different electoral environment. Scottish Labour would also hope that their Westminster recovery would presage a rebound in Scottish parliament elections due early in the next Westminster term. Scotland’s distinctive political environment may also make it easier for an incoming Labour government to defend its majority when seeking a second term. Conservative recovery in opposition won’t threaten Scottish Labour seats, which will turn instead on the fortunes of the SNP. Whatever the future holds, the SNP’s electoral collapse in Rutherglen makes one thing certain. After a decade dominated by one party and by one question – independence – Scottish politics is in flux. Change is in the air here, as it is elsewhere. By seizing that mood, Labour just took another big step on their long path back to power.