The question that kept occurring to me last week when I spent the afternoon in Uddingston after Nicola Sturgeon’s arrest was: what effect will it all have? The people I spoke to in the town where Ms Sturgeon has a house seemed remarkably unmoved by the news, and reluctant to shift their votes. It felt to me that the plates should be shifting, that there should be movement under my feet, the rumble of change. But instead: silence, stasis.

It looks like I was wrong though, or maybe just talking to the wrong people. A new Panelbase Poll for The Sunday Times, the first poll since Ms Sturgeon’s arrest, suggests support for the SNP has fallen to 34%, a drop of five points compared to Panelbase’s last poll in March, putting them level with Labour, whose vote share is up by three. Translated into seats, it would mean Labour get 26 MPs and defeat the SNP for the first time since 2010.

I’m tempted to say: woo-hoo, ha-ha, how funny, but saying woo-hoo, ha-ha, how funny would be childish and mummy tells me not to be childish. I’m also aware of the effect that the last 10 years has had on me, and you too probably. Before 2014, I would never have considered myself tribal or national or political particularly, but the fact that we were forced to pick a trench – the muddy trench of Yes or the muddy trench of No – meant a pretty fundamental change in the way Scottish politics worked, which we may only now be emerging from.

It’s important, obviously, to keep all of this in perspective, which is clearly what the Scottish Labour leader Anas Sarwar is trying to do. Responding to the poll, Mr Sarwar said he thought it indicated Labour had momentum but that there was still a hell of a lot of work to do; he also insisted his party was not complacent. This is definitely the right approach, particularly for Labour which is still living in the long shadow of Neil Kinnock’s We’re All Right! cock-up in 1992. Lesson: do not party too soon.

It's also striking how the fortunes of Ms Sturgeon and Boris Johnson have changed since the last general election in 2019, driven in a large part by Brexit. What we saw back then was that many, if not most, of the English voters who supported the Conservatives in traditionally Labour areas did so because they wanted to see Brexit happen, and many, if not most, of the Scottish voters who supported the SNP in traditionally Conservative or Labour areas did so because they wanted to see Brexit stopped. It also meant that Sturgeon and Johnson, although in opposition to each other, looked unstoppable.

But it’s only now, I think, that we can see that the seeds of the current situation were already planted in 2019. Many of the voters who supported the SNP then did so because they saw it as a practical way to stop Brexit and/or because they saw the SNP, and Sturgeon in particular, as competent. However, many of those voters – and I know this because I spoke to lots of them – were also still opposed to, or suspicious about, independence, and they agonised over whether voting SNP was the right thing to do. In that sense, 2019 wasn’t the beginning of a surge for the SNP, it was a high point.

And so it has proved. The SNP won 45% of the vote in 2019, but is now some 11 points lower than that because some of the voters who have lent their vote to the SNP are now returning to the other parties, or have already done so. Partly, this is because Brexit no longer has the power it once had as an issue to drive voter behaviour, but it’s also because it’s no longer credible to see the SNP as competent. Look at the list dear boy. Ferries. Deposit return scheme. Gender reform. Ferries. Drug deaths. Waiting times. Ferries. Ferries. Ferries.

The latest poll is undoubtedly a reflection of all of these factors but what it also appears to show is that the movement to Labour that’s happening among the softer SNP supporters has probably been underway for some time and the shift that’s been happening more recently is occurring almost entirely among harder Yes supporters. This is where it really starts to bite for the SNP I’m afraid; bits are falling off the rockface, and the obvious conclusion is that the phrase “You’re under arrest Ms Sturgeon” was the final straw for some people. The fact her personal ratings have also tanked would appear to bear this out.

But what’s also striking about this latest poll is what hasn’t changed, even now, and the fact that 34% of people are apparently still willing to vote SNP. You can see a similar phenomenon in England where some 28% of voters still intend to support the Tories and I’m tempted to say: who are these people and what on Earth will it take? The answer, probably, is that politics has always been like this: there is a streak of society that is loyal to a particular party and always will be, whatever the circumstances. As someone who has voted for all the parties at least once and happens to think that’s the best way to do things, I do not understand it and I don’t think I ever will.

However, the bigger point here is that the hardcore – and I spoke to a few of them in Uddingston who said that Ms Sturgeon’s arrest would make no difference to their support for the SNP – don’t in the end determine the result. For decades, there was a hardcore vote for Labour in Scotland and now there’s a hardcore for the SNP in Scotland and the Tories in England but no one’s in much doubt that the SNP and the Tories will do badly at the next general election.

Anas Sarwar and Scottish Labour are right to be excited about all of this – I am too – but Mr Sarwar is also right to be cautious and wary of being complacent because it’s clear that the hardcore will stay hardcore and he’ll be relying on the much softer middle of voters who are more likely to be influenced by events.

Will they switch back to the SNP in great numbers before the election? It seems unlikely. But Labour supporters know their history and they know that the party took its vote for granted in Scotland for a very long time – it was one of the reasons it collapsed. They must also know that it’s important, especially now when things are looking good, that they do not make the same mistake again.