SCOTTISH Labour anguish may seem like the basis for a niche psychodrama, but the implosion of the party of Donald Dewar and Gordon Brown is a hugely serious matter for anyone who cares about the future of the UK.

Even in 2011, when the SNP won a historic majority at Holyrood, Labour secured a respectable 31% of the vote. Viewed from today’s telescope, that result seems like the golden days. The same party came a humiliating fifth at the recent European election. As Labour slides, support for independence rises.

It is estimated that around 30% of Labour voters backed independence in 2014. That is why Yes managed to scoop nearly 45% in the referendum. The recent Lord Ashcroft poll showing a majority for independence was based on a larger chunk of Labour voters, 40%, rejecting the Union.

You do not need a PhD in Electoral Failure to work out why this is the case. If centre-left voters no longer see Westminster as a vehicle for progressive change, and conclude that Labour will not enter Government any time soon, it is inevitable that heads will be turned by an alternative. A combination of Boris Johnson, Brexit and the uselessness of Jeremy Corbyn is lethal for the Union. Exasperated Labour voters delivered Yes its polling majority.

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The latest episode in Scottish Labour’s tragicomedy, which played out in front of an open-mouthed media at the Edinburgh Festival last week, felt like a turning point. Leader Richard Leonard, despite his many shortcomings, has been staunchly pro-Union since taking up the post in 2017. Shadow Chancellor John McDonnell, a supposed left-wing ally, publicly knee-capped Leonard by suggesting a Labour Government would not block indyref2.

The effect of McDonnell’s calculated intervention, which sent a signal to the SNP that a Corbyn Government could work with the Nationalists, was to throw more fuel on the fire of Scottish Labour’s civil war. Some candidates signed a letter criticising him; others did not. Some MSPs put their names to a strongly worded statement; others declined. The party is a bottomless pit of idiocy.

The shadow chancellor also harmed Labour’s already questionable electoral chances on both sides of the border. The Tories will, with some merit, use the next general election to argue that Labour intends to do a deal with the Scottish Nationalists. At Holyrood, Ruth Davidson will taunt Labour that they cannot be trusted on the Union.

This matters because it will increase the sense of despair felt by Labour voters in Scotland who feel politically homeless. Around 20% voted Labour at the 2016 Holyrood election. It is this segment of the electorate that is the last line of defence stopping Scotland from becoming independent. Many of these voters prefer Nicola Sturgeon to Davidson.

I could write that Leonard is finished as leader, but I am unconvinced he ever started. He defeated MSP Anas Sarwar from the Left, but the Corbynistas who helped him replace Kezia Dugdale prioritise Corbyn over him. They want a Labour Government in London much more than they want one in Edinburgh. If that means cosying up to the SNP, and throwing Leonard under a bus, then so be it.

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Leonard is like an injured horse that fell at the first fence. His parliamentary group, a majority of whom voted for Sarwar, do not rate him. The public have never heard of him. And now the Left has abandoned him. He is a leader with one gear - reverse. He’s done.

Sarwar ran a lousy campaign in 2017, but his supporters were spot on about one of their warnings. They correctly argued that the left-winger would become a hostage to the Corbynistas and return Scottish Labour to the status of a “branch office”.

Here is one example. Despite Scottish Labour being “autonomous”, I understand that figures in Corbyn’s office (LOTO) have a say in managing the Scottish party's media and policy positions on constitutional matters, something Dugdale would not have tolerated. Alignment with the UK party is the objective. Leonard, a one star politician, is a follower rather than a leader.

Insiders also despair at the role played by Leonard’s chief of staff, Lesley Brennan, who is viewed as weak in her dealings with LOTO. Critics want Leonard to replace her with someone who is alive to the political dangers of being too close to Corbyn’s crew, and who is willing to defy LOTO. She is also said to have had a poor relationship with Scottish Labour general secretary Brian Roy, who is not seen by Leonard’s team as an ally. Roy's departure from his post was announced on Friday and a LOTO staffer is tipped to take over.

It should be noted that Scottish Labour’s problems did not begin with Corbyn or Leonard. The party won 56 seats at the 1999 Holyrood election; in 2016, under Kezia Dugdale, that tally fell to a pitiful 24. Labour first lost to the SNP in 2007 and have been led by the hopeless and hapless, but Leonard put his foot on the accelerator of decline.

His warring party is caught in a deadly tailspin. In May’s European election, Labour’s vote share fell to 9.3% and they were lucky not to come sixth. Senior party figures believe Labour will lose all seven Scottish seats at the next general election. At Holyrood, Leonard’s diminished tribe could crash to single digits.

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The SNP smell blood. If the UK has a risk register, the state of Scottish Labour should be flashing red. Once the strongest brand in Scottish politics, it has become sub-prime, the political equivalent of the pre-2008 Lehman Brothers. Leonard’s party is galloping towards the cliff, and the only question left is whether the UK will be dragged with it.