I VOTED SNP. Those are words I’ve heard so many times over the last few days, often from people who’ve never voted for the Scottish nationalists before and, to be honest, thought they never would.

But that’s where we are now: thousands of Scots who are unionist, or inclined towards the union, voted for the nationalists on the night and Nicola Sturgeon couldn’t believe her luck, particularly when it brought down Jo Swinson. As the Liberal Democrat leader lost her seat, the First Minister laughed and cheered and clenched her fists until the skin turned white. Then she realised she’d been caught on film and tried to look more magnanimous. Too late. We saw.

Obviously, unguarded moments like that one on election night can reveal what’s really going on in a person’s head, but there’s also quite a lot to be learned from what Ms Sturgeon has said since the election, as well as from the speeches Boris Johnson made. Both leaders benefited from voters doing what they wouldn’t normally do. In the case of the PM, it was Labour voters in the north of England voting Tory, and in the case of the First Minister, it was unionist voters supporting the SNP. It brought Mr Johnson a win and Ms Sturgeon a win within a win.

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But, if Mr Johnson and Ms Sturgeon are not to come a cropper, both of them are going to have to understand what’s really going on here. 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. In that sense, they voted for an outcome rather than a party.

The conversations I’ve had in the last few days with unionists who voted SNP have revealed a bit more about what that means. Most of them are still opposed to, or suspicious about, independence, and they agonised over whether voting SNP was the right thing to do. But, in the end, they concluded Brexit and a Tory government was the greater evil. One voter told me his vote for the SNP was in no way a pro-SNP vote, simply a way of ensuring a Brexit supporter did not win in his three-way marginal. “I’m not a nationalist and never will be,” he said.

However, this election was never going to be just about Brexit, and the unionists who voted SNP were aware of the other possible consequences of their vote. In the last bit of the campaign, the SNP appeared to play down independence and play up “Stop Brexit”, but voters knew or suspected that Nicola Sturgeon would interpret support for her party as support for another independence referendum, which is precisely what happened. Admittedly, the First Minister did say that not everyone who voted SNP supported independence, but she also said her party’s success provided a renewed, refreshed and strengthened mandate for a new Scottish referendum.

This did not please the SNP-voting unionists I spoke to, even though they knew it was likely to happen. One said to me that Ms Sturgeon’s use of the election result was cynical and had made her less likely to vote SNP a second time. It might also have helped if the First Minister had acknowledged the subtleties, nuances and conflicting emotions that led Scottish voters to act in ways they never had before, rather than rushing to claim a mandate for a second referendum.

Weirdly – because he’s anything but subtle – Boris Johnson actually did a better job of talking about this phenomenon of “lent” votes. He could have sounded triumphalist; he could have clenched his fists and cheered at the defeat of Labour candidates in traditionally Labour areas.

But instead he said that he recognised some voters’ hands might have “quivered” before they put their cross in the Conservative box. He also said he knew that many of those voters probably intended to vote Labour next time round. Rather than claiming the voters as Tories, it was an acknowledgement of what was actually going on with some people, and Nicola Sturgeon should have done something similar in a lot more detail and with a lot more humility.

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Ms Sturgeon and her advisors should also be cautious about what they take from this for the future. As my SNP-voting unionists explained, they voted the way they did in the general election mostly because they felt they had no choice. They were in constituencies where, because of the first-past-the-post system, voting SNP was the only way to maximise the chances of thwarting the Tory and voting against Brexit. Truthfully, they would rather have voted Labour or LibDem and in a proportional system, they would have done. But instead, because of the system we have and with Brexit as the main concern, reluctantly, fretfully, and with a heavy heart, they voted SNP.

Obviously, the same rules will not apply when the 2021 Scottish general election comes round: under proportional representation, voters will be free to vote for a party they believe in. This means many of those who voted SNP in 2019 because of Brexit and Boris will revert to their previous choices in 2021, not only because Brexit will presumably no longer be the issue it once was but because voters will understand that independence really will be on the ballot in 2021 and there’ll be no question about how their vote will be used by the SNP.

Not everyone will behave in the same way of course. One of the voters I spoke to, a man who voted No in 2014 and SNP this year, said he wouldn’t rule out supporting a future independence referendum if it was the lesser of two evils.

However, for other unionists who have just voted SNP, the 2021 Scottish election will be a chance to vote against independence just as the 2019 UK election was their chance to vote against Brexit. What this means is that, far from being the beginning of a surge for the SNP, the election we’ve just been through could be a high tide. Maybe the First Minister gets this. Maybe she realises some of the votes she won last week are only on loan. And maybe she should think about it a bit more before she clenches her fists in triumph.