BIT of news from the doorstep. My postie was telling me the other day what the election means for him and his colleagues. The good news: they’re going to be paid a bit extra to deliver all the political leaflets; the bad news: there will be lots more long shifts in the cold and wet. It makes you wonder why the parties are even bothering. Leaflets aren’t going to change minds this time around. All that matters is independence and Brexit.

The trouble is, central as those two issues are to the election, it’s hard to tell precisely how they are going to affect voter behaviour. The broad-brush polls show the SNP where they’ve been for a while – at over a third of the vote – with the Tories dropping by a quarter, and if you were to apply those figures evenly across Scotland, the Conservatives would lose all but four of their seats.

But it’s not as simple as that, is it, because the primacy of independence, in particular, has created a more complicated situation and a greater willingness by voters to switch parties to secure the outcome they want.

This doesn’t apply to the SNP obviously – if you support independence above all else, you won’t lend your vote to another party – but voters who oppose independence have a choice and can switch support to maximise the chances of defeating the SNP. It happened in 2017 and the Tories in particular benefited.

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What has complicated matters since then is Brexit. In 2017, some unionists were prepared to vote Tory to inflict a defeat on the SNP, but, this time round, many unionists who voted Remain will be concerned that voting Tory means supporting Brexit. What will these voters do? Are they so horrified by Brexit that they will switch from the Tories, risking more SNP wins? Or are they still so worried by independence that they will stick with the Tories and risk Brexit?

I suspect that, gruesome though Brexit is, this tactical unionist vote for the Conservatives will prove to be more robust than we think it is, for a couple of reasons. First, in many key Scottish constituencies, it’s a one-on-one fight between the Tories and the SNP. In other words, if you’re a unionist/remainer and live in a constituency like Gordon, Stirling, or South Perthshire, or North Perthshire, Central Ayrshire, Edinburgh South West, or Lanark, your only choice for an anti-SNP vote is to vote Conservative. Switch from the Tories to support a party that’s both anti-independence and anti-Brexit and you risk letting the SNP win.

Secondly, there’s a good chance that unionists who are agonising over how they should vote this time – anti-independence or anti-Brexit – will be influenced by the SNP’s campaign so far. If the First Minister herself is saying that the election is all about independence, and any SNP victories will be used to support the case for it, what’s the point in casting your vote based on Brexit? The Scottish Conservatives’ promise of a referendum-free future could also be a factor here – it was a rare clever move in an otherwise lacklustre campaign.

Other unionists/remainers are obviously considering whether to vote Liberal Democrat and in at least one constituency – North East Fife – this could have an effect; the Lib Dems were just two votes behind the SNP there in 2017. But in every other SNP seat, the Lib Dems are in a distant third or fourth place, meaning that if you’re a remainer convinced by Jo Swinson’s strong pro-EU message and vote Lib Dem, you effectively leave the struggle over Scottish independence to other parties and potentially let the SNP win.

Naturally, Ms Swinson would deny this and she did deny it when I asked her about the issue a few weeks ago. There are seismic things happening in politics, she told me, and a party can win from third place. She also said some of her party’s private polling showed the Liberal Democrats had a chance of doing well in Ross, Skye and Lochaber, the seat held by Ian Blackford, the SNP leader in the Commons. The electorate is more volatile than it was, she said, so don’t discount us.

Was she being over-confident? Probably, although, having said that, the defeat of Alex Salmond in 2017 proved no SNP figure is too big to fall, even if Mr Salmond did lose at the height of the Tory surge and frustration with SNP talk of a second independence referendum. A high profile like Mr Blackford’s, or indeed Ms Swinson’s in East Dunbartonshire, can also work both ways: for every voter who is pleased to have a leader on their patch, there will be one who is turned off. Those two seats could be more volatile than we expect.

As for the remaining battles between Labour and the SNP, they are perhaps a little easier to call. There are some seats in which it was a close-run thing between Labour and the SNP last time – Coatbridge, Kirkcaldy, Midlothian, Rutherglen, Glasgow North East and Glasgow South West – but if Labour couldn’t win those seats decisively in 2017 at the peak of tactical voting against the SNP, then they are unlikely to win them this time, especially with a less-then-inspiring Scottish leader.

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Exactly how all of these factors will play out, in the end, is hard to predict for sure, but I suspect the complicated interaction of Brexit and independence will mean less change than the SNP hopes for. They will probably take five of Labour’s seats, but I think the Tory vote will hold up much more, leaving them with eight or even nine. As for the Lib Dems, they’ll stay where they are, or gain one or two.

Whatever happens, the seats to watch are the 16 I’ve named above because they are the ones in which unionist/remainers wrestling with the issue of Brexit can have the greatest influence. Undoubtedly, some of those unionist/remainers will vote with their anti-Brexit hearts and that will be enough for the SNP to win some more seats. But the SNP should remember this as well: some voters support unionism with just as much passion and stubbornness as others support independence, and they are willing to vote that way.

Where does that leave us then? Earlier, I asked two questions. Will unionist/remainers be so horrified by Brexit that they will switch from the Tories, risking more SNP wins? Or are they still so worried by independence that they will stick with the Tories and risk Brexit? I suspect the answer to both questions is this: for many voters, voting for a party that supports Brexit may be a risk they are willing to take to try to keep the SNP at bay.