BBC Alba, Scotland’s Gaelic language channel, is not normally required viewing for the political classes. This week, however, Lib Dems across the country were seeking it out on Freeview.

The channel last night aired a documentary on Charles Kennedy, the former Lib Dem leader who stood down in 2006 after acknowledging his struggle with alcoholism, which persisted until he died in 2015 at the age of 55.

Three weeks before his death and after 32 years as MP for a Highland constituency – latterly called Ross, Cromarty and Skye – he was defeated in the 2015 General Election by Ian Blackford, now Westminster leader of the Scottish National Party and a man rich in hyperbole, bombast and bluster.

No politician could be more different in style and substance from Charles Kennedy – a man of courtesies and humour with a sharp political edge; a skilled debater who believed in the power of argument, who was respected by his political friends and most foes, which was reflected in the programme’s title: Charles Kennedy: A Good Man Speaking.

In its latter stages, the documentary described the vile campaign Charles was subjected to in the weeks before his death. Rather oddly, there was no direct reference to the instigator, Ian Blackford. When questioned about this, BBC Alba said that the programme was about Charles Kennedy, not Ian Blackford. That is a fair point. To have over-emphasised the repellent features of the 2015 election campaign in Ross, Cromarty and Skye might have detracted from the programme’s laudable objectives; to give a rounded view of Charles’s life, his background, his strengths, his flaws.

Nonetheless, any description of Charles’s political demise without reference to Blackford is a bit like reviewing The Exorcist without mentioning the devil. For this was a campaign of shame which should be neither forgiven nor forgotten; certainly not for as long as Mr Blackford occupies a place on the political stage.

What was so striking about the SNP’s vile campaign was that it was entirely unnecessary. The writing was already on the wall for Kennedy’s political career, like almost every other Scottish MP of a non-Nationalist persuasion. The 2014 referendum transformed dividing lines in Scottish politics, and not in a good way. While a 44.7 per cent vote did not deliver independence, it created a voting bloc sufficient to win almost every constituency in Scotland. That is the political rut in which the country remains stuck.

The Cameron-Clegg Coalition had not played well in the Highlands where the Liberal vote had retained its radical connotations and had remained the anti-Tory vote of preference. While Charles still had a high degree of affection and there was an understanding of his problems, patience was wearing thin among some voters. Maybe it was time for Charles to pack it in without waiting for the public execution. But then, what else would he have done? All in all, it was a bleak picture pointing to inevitable defeat.

Enter Ian Blackford, as SNP prospective candidate in January 2015. Blackford, a merchant banker for Deutsche Bank, re-cast himself, entirely unconvincingly, as a Skye crofter. He immediately adopted the unsubtle dog-whistle campaign hashtag: ‘Where’s Charlie?’ It wouldn’t have required much to find exactly where Charlie was, both physically and mentally. He was mourning the death of beloved parents; grieving the early demise of his best friend; fighting a horrible disease; struggling to hold a family together.

As soon as Blackford launched the ‘Where’s Charlie?’ slogan, I wrote that it seemed ‘a clear attempt to personalise the contest on grounds which are undesirable and unnecessary. Mr Kennedy’s fragility is scarcely a state secret. On top of that, he is coping with a string of tragedies and losses.’

In response to the whistle, Blackford’s rottweilers were out the traps. One of his closest associates, Brian Smith, convener of the SNP’s Skye branch, wondered online if Charles, ‘has “a problem” that stops you going to Westminster?’ Up to election day, Smith bombarded Charles’s social media sites with abuse, describing him as ‘our own arch-Quisling’.

Smith was soon one among many Cybernats. One of Charles’s constituency staff had to work full-time on deleting social media abuse. There were vile anonymous messages attached to Charles’s car and pushed through his letter-box. When he returned home after the confirmation of his defeat, the bins had been emptied across his driveway. The level of sheer cruelty was beyond comprehension – and all totally unnecessary in terms of the election’s outcome.

The whole way politics is conducted in Scotland has changed beyond recognition and anyone deluded into believing there is anything liberal or progressive about that should consider the case study of Blackford versus Kennedy. They might be reminded that other people’s Nationalisms invariably look more attractive from a safe distance.

Charles Kennedy, the good man, died three weeks after losing his seat. The poison of the campaign did not kill him but it robbed him of peace and dignity in the last months of his life. Democratic politics need never be like that. As one of Charles’s staff, David Green, told the programme: ‘Because you don’t believe in a certain constitutional outcome for the country you deeply care about, that doesn’t make you a Quisling or a traitor… It just means you have a different viewpoint.’