A miniature sporting curiosity is re-enacted each year that conveys integrity and stewardship in the face of shallow commerce. It’s when the gnarly hand of an engraver is seen to inscribe the name of golf’s Open champion on to a sacred claret jug. At what point does this master craftsman get the nod to begin his work? His is a task that doesn’t reward haste and yet he can’t tarry too long. This little ritual sprang to mind when Boris Johnson became Britain’s latest prime minister. In it, the silent engraver is beginning to inscribe the words “Scottish independence” even as Johnson’s name is being announced.

In the weeks since it almost seems as though Johnson is eager to fulfil one of the expressed wishes of England’s Brexit supporters. In several polls they signalled their willingness to sacrifice Scotland as a price worth paying for securing Brexit. This seems to have lodged itself subliminally in the minds of Tory MPs at Westminster. In recent weeks they have been seen to observe a rather less edifying ritual of their own. Thus, whenever Ian Blackford rises to respond to the latest convulsion on the withdrawal agreement a signal is emitted at a pitch that can only be picked up by English Tories. As soon as the SNP’s Westminster leader opens his mouth to speak, they rise as one and depart the chamber. At other times they talk loudly over him in an adolescent attempt to convey indifference and disdain.

Seasoned Scottish MPs who are accustomed to the rough exchanges of this place have been astonished at this behaviour. Social alliances between the two parties, born of bar-room conviviality and membership of the same special interest clubs, have been a feature of the past few Westminster terms.

A chill has been manifest in the loutish behaviour of many Tory MPs and their disrespect of Blackford in the chamber

One SNP MP, part of the 56 who took all but three of Scotland’s seats in 2015, told me of how genial he had always found the Tories to be. “They are far more civilised and less hostile and tribal than the Labour contingent,” he told me a year later. “They rarely allowed political beliefs to get in the way of human engagement, whereas Labour politicians, with whom we have much more in common doctrinally, are often sullen and guarded.”

Part of this of course had its roots in something more prosaic. Recognising the strength in numbers of the SNP intake, Conservative MPs were eager to solicit support from among the new group when a prized committee chairmanship was up for grabs. The horse-trading was often conducted in Westminster’s social gathering places and alliances born of mutual respect, if not friendship, were born.

A chill became apparent, though, with Johnson’s accession and has been manifest in the loutish behaviour of many Tory MPs and their studied disrespect of Blackford in the chamber. “Some of it has been truly embarrassing,” another Scottish MP told me last week. “And you can see it in the eyes of some of the older and more experienced Tories, like Kenneth Clark, who seem aghast at this.”

Johnson himself chose to deepen this sense of a party that is now past caring about the prospect of an independent Scotland. Last week he admitted that he was in no mind to grant the Scottish parliament any role in approving the withdrawal agreement. Yet the bill will carry legislation into 17 devolved areas with the Scottish government claiming that it will actually impact on a further 44. His intentions run contrary to the Sewel convention of Westminster not normally involving itself in devolved areas without the consent of Holyrood. It also undermined Johnson’s decision to award himself the imaginary cabinet portfolio of minister for the union in the style of Idi Amin declaring himself to be the king of Scotland.

The departure for good of all Scottish MPs would make it almost impossible for Labour to entertain any prospect of power

Respecting the Sewel convention would never have been near the top of Johnson’s political concerns, so why make a show of belittling Holyrood like this? In public he maintains the unionist line on Scottish independence by refusing to countenance any talk of a second referendum. Other Tories believe, though, that he would find it difficult to refuse a second independence referendum if there were to be another clear pro-independence majority at the next Scottish election in 2021. And certainly not if the electoral campaign were a manifesto for independence. Ruth Davidson, who recently resigned as Scottish leader, was the Tories’ most potent weapon against independence, but she’s no longer around to bend his ear on the issue.

As ever with Johnson, there are pragmatic reasons for finally letting Scotland go, which resonate with an almost frightening level of personal ambition. The departure for good of all Scottish MPs would make it almost impossible for Labour to entertain any prospect of power in the foreseeable future. This would leave him virtually unopposed as prime minister of England for a generation.

Those polls indicating that a majority of English Brexiters would be happy to lose Scotland in the process merely reflected the rhetoric of Jacob Rees-Mogg and the European Research Group. Over the past three years their loudest cheers have come when they channel Trafalgar, Waterloo and cry God for Harry, England and St George. When they talk about taking back control and being free once more to make their own laws everyone knows these are English laws and English control. If only losing Northern Ireland were just as simple.

Once, a Tory prime minister would have been horrified at the prospect of going down in history as the one who lost Scotland. But at this time in this England Johnson would quickly be forgiven if he were also the man who delivered its independence.

• Kevin McKenna is an Observer columnist