This, in case you didn’t know it, is the week Labour makes a clever strategic move, a sort of pre-emptive strike that both Anas Sarwar and Keir Starmer hope will do several things. First, undermine a key Tory tactic; second, outmanoeuvre the SNP; and third and most important, win them the next election.

The first part of the plan happens at 10.30am today when Mr Sarwar, the Scottish leader, delivers a Fabian Society lecture at Westminster. The speech is ostensibly about Mr Sarwar’s policy plans for Scotland but the important bit will be his hard-line promise that Labour will not do a deal with the SNP in the event they end up short of a majority at the next election.

After making the speech, Mr Sarwar will then have meetings with Sir Keir and the shadow cabinet with a view to getting their story straight: no deal with the nationalists, no to another referendum, and possibly some procedural guarantee at conference designed to convince members and voters they really mean it. Sir Keir will also be underlining the promise himself. The message, some two years before an election, is clear: deal with the SNP? Never.

You can see why they’re doing it. Seven years ago. in the campaign for the 2015 election, the Tories claimed Labour would do a deal with the SNP and sacrifice the union to get Miliband into Number Ten. You may also remember those striking posters showing the Labour leader in the top pocket of a giant Alex Salmond. It was a simple and memorable image. Whatever you think of them, the Tories always have the best posters.

What’s more, the results of the general election seemed to justify the Tory strategy. There was a late swing from Labour to the Tories and analysis by the likes of the pollsters Survation suggested a significant number of voters were sufficiently worried about a hung parliament and the possibility of a Labour/SNP deal that in the end they decided to vote Tory, possibly reluctantly, and possibly with a heavy heart.

There were some senior figures in the Labour party at the time who could have said “I told you so” – people like Douglas Alexander who argued early on that the party had to be firm on ruling out an SNP deal. In fact, the Labour leadership was pretty slow to wake up to how effective the Tory line of attack was, and it wasn’t until just a few days before the election that they finally ruled out a confidence and supply agreement with the SNP. By that point, it was probably too late.

The obvious fear is the same thing could happen again, which is why Labour is rolling out its strategy now, including Mr Sarwar’s speech at Westminster. What it looks like is that Mr Alexander and others are winning the argument this time: the only way to deal with the “SNP deal” problem, they say, is to get in early, be absolutely clear it will never happen, and therefore neutralise the Tory tactic before it can get going.

On the face of it, the strategy makes sense – indeed, the Tories have already taken their 2015 campaign off the shelf and dusted it down for another go. Writing in The Daily Mail the other day, the former Cabinet minister Matt Hancock said the only viable alternative to a Conservative government was a coalition between Labour and the SNP. The risk, he said, was a grubby coalition deal that sold the union down the river.

However, the question for Labour is whether the early promise not to do an SNP deal will actually be enough. The impression last time was that Miliband was dragged into making the promise – possibly because he knew that the Tory accusation was true and he might indeed have to rely on the SNP to get into power. The party’s focus groups also showed that, even when he made the promise and said 'no deal with the SNP', voters didn’t believe him.

The new Labour strategy by Starmer and Sarwar does at least deal with the first problem of appearing reluctant to rule out a deal – they are both getting in early and saying it now, two years before an election. The question of believability is another problem entirely. There will be many voters who will hear Labour’s promise and still conclude that, when the crunch comes, they would do a deal anyway. Maybe that’s because of cynicism about politics. Or maybe it’s because they’re probably right.

Whether the strategy will work also depends on two types of voters. The first are those Tories who worried about an SNP deal and went for the Conservatives with a heavy heart. Call them the reluctant Tories. The second category are the SNP supporters who have proved remarkably loyal through all the travails of the Scottish government. Call them the stubborn nationalists.

Both these groups may hold the key to the next election depending on what they do, and there’s some cause for Labour hope. First, the reluctance of the reluctant Tories may be much stronger next time because of the state of the Tory party and the leadership of Boris Johnson. There’s also some evidence of a Labour revival in Scotland under Sarwar’s leadership, although the switchers appear to be coming from the Tories and the Lib Dems rather than the SNP. Those stubborn nationalists are still pretty stubborn.

The nightmare scenario is that Labour recovers a little in Scotland but not enough and that the Tory scare tactics about an SNP deal don’t work quite as much as they did in 2015 but still have an effect. All of this seems possible – the Tories are considerably weaker than they were seven years ago and the SNP is also no longer riding the post-referendum wave they were in 2015. Both parties are not what they were and this gives Labour a chance.

However, if enough stubborn SNP voters stay stubborn and enough reluctant Tories do vote Tory in the end, it may end up with Labour as the biggest party but short of a majority. For Labour, this is the nightmare: too weak to do what they want to, or forced to do what they don’t want i.e. a deal with the SNP. The SNP on the other hand win either way: either a weak Labour government or another Tory government make it easier to push their case for independence and perhaps even achieve it.

For the rest of us ordinary voters – including some reluctant Tories and stubborn nationalists – the prospect of a Labour government of any kind will probably come as a huge relief. But a minority government will also be a significant test. Mr Sarwar and Sir Keir will be spending this week promising us that an SNP deal will never happen. The next election may reveal if they are men who keep their promises.

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