As Scotland takes in the news that Boris Johnson is the new prime minister of the United Kingdom, there have been at least three significant responses north of the border, none of which will be much to Westminster’s liking.

The first is incredulity that a person whom many Scots judge to be a duplicitous buffoon has been “elected” to the most powerful office of state in the land. As recent polling has confirmed, Johnson is held in even more popular contempt in Scotland than his fellow arch Brexiter Nigel Farage, who famously fled from Scotland a few years ago after a fracas of protest at his appearance outside a pub in the Royal Mile in Edinburgh.

There is already a sense, however, that disbelief is beginning to metamorphose through a slow burning fuse into cold outrage and deep anger. This has been fuelled in part by an eccentric process that has handed power over the destiny of the UK to a small and entirely unrepresentative Tory membership (just over one-tenth of one per cent of the British population) who then, in predictable fashion, duly agreed to support the unthinkable as party leader and prime minister. Another factor should not, however, be underestimated – the list of right-wing ideologues who will sit around the cabinet table in Downing Street. Most of the names represent a metaphor for the chasm that now exists between Scottish political values and the political culture that flourishes today in many parts of England.

Most Scots since the 1970s have favoured social democratic policies with a leftish flavour. A clear majority also voted to remain in the EU in 2016. Now this electorate is presented by an array of hard-right Brexiter zealots holding key positions in the British government. It would be difficult to think of a bunch more likely to increase Scottish disenchantment with “our precious union” (© T May).

The second reaction has come from the SNP and those who espouse the cause of Scottish independence. Of course, their deeply hostile public responses to the Johnson coronation were entirely predictable. In private, however, the independence camp must be in celebratory mood. For them, Christmas has come early. The UK is now led by the best recruiting sergeant for the cause of Scottish independence since the days of Margaret Thatcher, she who was dubbed by the late Donald Dewar as the “mother of the Scottish Parliament” established on the back of reaction to her deeply unpopular policies.

Johnson is the very incarnation of everything Scottish nationalists loathe in English right-wing Tories: foppish, rich, privileged, incompetent, xenophobic. They will have enormous fun at his expense in the coming months as they milk the opportunity afforded by his election to try to batter the Union to death both within and outside Westminster.

Ruth Davidson faces the prospect of seeing everything she has done to rejuvenate Conservatism in Scotland unravelling. Photograph: Ken Jack/Getty Images

And then there are the Scottish Conservatives. Some did their best to avoid the horrendous outcome which has now been visited upon them through the aptly named Operation Arse. They failed. Johnson triumphed over them. The leader of the Scottish Conservatives, Ruth Davidson, now faces the prospect of the project designed to rejuvenate Conservatism in Scotland falling apart before her very eyes. This was not the doing of either the SNP or Labour, but of English Tories hell-bent on having Johnson as their champion, the only man who could save them from being overwhelmed by the Brexit party tsunami. It will be most interesting to see how Davidson’s well-publicised talents cope with this thorny problem.

In his first brief public confrontation with Johnson, the SNP Leader in Westminster, Ian Blackford, described him as “the last prime minister of the United Kingdom”. It was a public admission of the sheer joy in SNP ranks at being presented with the political gift of Johnson’s elevation. Blackford just stopped short of rubbing his hands in glee. But could the union between Scotland and England actually come to an end during Johnson’s watch?

There are omens. The most recent opinion polling suggests the gap between those for and against Scottish independence has narrowed to a close 49 per cent for “yes” and 51 per cent for “no” – and this before any Johnson effect is taken into account. Pollsters reckon that Johnson as PM could add a few more percentage points to the Yes vote.

Then there is his vow to deliver Brexit by October, even at the cost of no deal, a scenario which would have potentially serious consequences for the Scottish economy. If no deal happened, the threshold of risk in people’s eyes might therefore shift dramatically to independence as a better option, with the prospect of rejoining the EU afterwards.

There are also longer term forces to be taken into account. English nationalism, red in tooth and claw, is now a political reality. Its message is England first, and with that scant regard for the needs or interests of the other three nations in May’s “precious union”. Apparently English nationalists are even prepared to see the end of the union if that is the cost of achieving Brexit. This writer has long felt that the English factor would eventually be more decisive in the collapse of the union than forces emanating from Scotland.

However, it is likely that Johnson will be spared the humiliation of going down in history as the UK’s last prime minister. Granting the authority to hold another referendum on Scottish independence is a power reserved for Westminster. A Johnson government will be resolutely opposed to ever agreeing to such a concession. Equally, the intrinsically canny and cautious Scottish government, loth to alienate moderate voters, is unlikely to contemplate employing “other” methods, at least in the short run.

Johnson is more likely to be evicted from Downing Street by a vote of no confidence and defeat in a general election than by an existential crisis in the union. Nevertheless, future historians might well consider recent events as an important milestone on the road to eventual Scottish independence.

Sir Tom Devine’s books include The Scottish Nation: 1700-2007