At various points in the history of political parties their activists and supporters face a choice, a fork in the road.

Back in 2004 the Scottish National Party, now the UK’s most successful political movement, faced such a choice, John Swinney having resigned after a few troubled years at the helm.

Nicola Sturgeon initially threw her hat into the ring, as did, quixotically, Mike Russell, but Roseanna Cunningham was widely considered the frontrunner. Although no longer much of a left-winger, she had a reputation as a firebrand, “Republican Rose”.

This disconcerted many senior Nationalists, and when Ms Cunningham gave a less than assured performance on the BBC’s Question Time, a feeling grew that the SNP had to pursue what one MSP called an “ABR strategy – Anyone But Roseanna”.

Thus the king over the water, Alex Salmond, was persuaded to run and the rest is history. I mean no disrespect to Ms Cunningham, who’s subsequently proved a capable minister, but it would be difficult to argue that the party would have fared as well had she, rather than Mr Salmond, been elected leader. The SNP, in other words, chose wisely.

Today Labour faces a similar choice, another “fork in the road” (as Andy Burnham has called it), with one Shadow minister declaring that it has “to be anyone but Corbyn”. If he won, added the anonymous MP, Labour would face “electoral oblivion”.

But all the signs are that Labour won’t choose wisely, but rather opt for “authenticity” over electability. Yesterday a poll showed that a Corbyn victory would worsen Labour’s chances in 2020, and indeed even the man of the moment doesn’t consider himself a credible next Prime Minister. Introduced as such at one of his Scottish rallies, he and everyone else laughed at the idea.

In the context of the new normal, however, highlighting this reality achieves very little, particularly when those doing so are laden with baggage. Tony Blair’s warning of electoral annihilation barely had an impact, while yesterday Gordon Brown took to a London stage to warn that it was “not an abandonment of principles to seek power”. I can’t help feeling, however, that high-profile “interventions” from the former Prime Minister, however cogently argued, are subject to the law of diminishing returns.

Meanwhile Kezia Dugdale, decisively elected on Saturday as the new Scottish Labour leader, has rolled back a little on her previously articulated fear that the party would end up “carping from the sidelines” if led by the Member for Islington North, and given his obvious momentum she had little choice.

But Ms Dugdale isn’t the only one triangulating her way through difficult political terrain. Faced with the prospect of victory even Mr Corbyn has toned down his previous opposition to the European Union, rebutted claims that he intends to restore Clause 4 and, most recently, has made it clear that he’ll “stand up” for businesses that “want to co-operate and innovate for the public good”. Ironically, even the leadership candidate widely viewed as “authentic” and “consistent” realises that ideological purity does not a successful politician make.

Even so, negotiating her way through the Labour Party’s ever-complicated Anglo-Scottish leadership structure will be one of many challenges facing Ms Dugdale. Already Ian Murray, the Shadow Scottish Secretary and sole Scottish Labour MP, has suggested he might not serve under a Corbyn-led Labour Party, presenting the party with an obvious personnel problem should that come to pass.

Ms Dugdale will also have to contend with the SNP cosying up to Mr Corbyn in order to consolidate its place to the left of the Scottish Labour Party and expose its new leader as inauthentic, i.e. insufficiently left wing. And when the backlash, both within and outwith the Labour movement, inevitably occurs, Nationalists won’t attack Corbyn but argue that the Blairite “virus” is clearly incurable and thus independence remains the only option for left-wing Scots.

On top of all that Ms Dugdale will have to find a way of regaining a voice in the debate, something the party lost during the independence referendum. As the former Canadian politician Michael Ignatieff observed in his memoir, Fire and Ashes: Success and Failure in Politics, “once you’ve denied people’s standing, you no longer have to rebut what they say. You only have to tarnish who they are.”

Usefully, the new Scottish Labour leader acknowledged that uncomfortable reality in her short but thoughtful victory speech on Saturday afternoon. “It’s not so much that they don’t like what they hear,” she said of a large chunk of the Scottish electorate, “they’ve stopped listening to us altogether.” Even those willing to give the party a hearing, she added, “tell us they don’t know what we stand for anymore”.

Conversely, those parties and individuals who do possess “standing” in the eyes of voters are generally immune to normal political scrutiny, thus the SNP can soar to 62 per cent in the polls despite a mediocre record in government, and Mr Corbyn can find himself with a 32-point lead despite holding political views – particularly on foreign policy – which place him well beyond the comfort zone of all but the most left-wing voters.

Scottish Labour activists comfort themselves with the hope (and it can only be a hope) that at some point the SNP’s uncanny (and long-standing) ability to suspend voter disbelief and convince supporters that radical change is just around the corner will come to an end. Indeed, this week Nicola Sturgeon will set out yet another “bold programme”, but we’ve been here many times before and it’s usually nowhere near as “bold” as the rhetoric suggests.

But then the National question has entirely rewritten the rules of the political game, making life for opposition parties such as Labour increasingly intolerable. All Ms Dugdale can hope to do is carve out a niche in which she can plug away at a few resonant policy issues while attempting to highlight weak points (and there are many) in the Scottish Government’s record. There still exists a core Labour vote that doesn’t trust the SNP and she has to keep them on side.

Tacking to the left in order to keep up with the Joneses (Corbyn and the SNP) would be a misreading of the current political dynamic, and while not doing so might not produce an immediate political reward, it is in reality the only tenable option for both the Scottish and UK Labour parties. For although Blairism has lost standing, its central lesson still applies: elections are won not from the left but from the political centre ground.

And, ironically, the SNP’s recent success proves that point, for when it chose Mr Salmond over Ms Cunningham back in 2004 it made a hard-headed calculation about who was most likely to restore the party’s electoral fortunes. It worked, and crucial to the success of Messrs Salmond and Sturgeon has been a pragmatic, centrist approach to politics. As Gordon Brown put it yesterday afternoon, “there is nothing progressive about being powerless”.