The uninitiated, on first encountering an SNP conference, might think that they were already stepping on to independent turf and that only the flourish of a civil servant’s pen was required to make it official. After two or three days of being held in the embrace of such boundless optimism you sometimes find yourself desperately seeking a dose of misery just to feel normal and Scottish once more; a Pink Floyd album perhaps, or a video of Great Scotland World Cup disasters.

Yet, courtesy of Theresa May’s constitutional intervention, the waves of optimism washing over SNP delegates at the party’s conference in Aberdeen this weekend were turned into something approaching certainty. In stating her refusal to sanction a second referendum the day after Nicola Sturgeon had finally expressed her intention to seek one, the prime minister gave the SNP a gift.

In doing so, May looked like an elderly schoolteacher spelling out the terms of detention to an errant pupil: “You can go home when I say you can go home.” Of course, she would have felt that she was occupying safe constitutional ground. The Edinburgh agreement, struck before the first independence referendum, requires the approval of No 10 to expedite the transfer of constitutional powers to enable a referendum on independence. Yet, on Thursday, May seemed merely to be haggling over the date of the referendum rather than its legitimacy.

Thereafter she and her two Scottish representatives – Ruth Davidson, the Scottish Conservatives leader, and David Mundell, the Scottish secretary – fell back on to shakier ground. They questioned the mandate of Scotland’s first minister amid flimsy rhetoric about there being no majority of support in opinion polls for a second referendum. Such blithe aspersions, though, fail to acknowledge that the 2015 Westminster election and the Holyrood election the following year were as clear an indication of the will of the Scottish people as you are likely to get.

In 2015, the SNP returned 56 out of 59 Scottish MPs to Westminster. In 2016 the party became the first in the history of Scottish democracy to gain more than 1 million votes as it stormed Holyrood again with 47% of the ballot. In each of these elections the SNP fought on a manifesto that included the pledge to seek another referendum if material circumstances changed in the UK. Even the dogs in the street know that following Brexit and the fact that 62% of Scottish voters elected to remain in the EU, material circumstances have changed significantly. The Conservative political commentator and former MP Matthew Parris freely admitted so later the same evening on the BBC’s Question Time.

In justifying her position, the prime minister stated that now was not the time to hold a referendum, when we all needed to work together to secure the best deal for Britain in the Brexit negotiations. This one won’t sail either, as, in the words of Sturgeon, up until now, “our efforts at compromise have been met with a brick wall of intransigence”.

With each ill-advised statement on the sovereignty of Holyrood, May has merely strengthened the case for Scottish independence. It doesn’t matter that Sturgeon has yet to indicate if an independent Scotland would seek early membership of the EU. What has triggered the call for a second referendum has been the high-handed and disdainful attitude of the UK government in refusing to work with Scotland over Brexit and its seeming determination to pursue a hard Brexit with no access to the single market.

That the prime minister has opted to use the future of EU nationals living in the UK, including many in Scotland, as a bargaining chip with the remaining 27 member states has strengthened Sturgeon’s conviction. The Tory government in sticking to its hardline stance on this has begun to resemble the political wing of Ukip.

In any debate about independence, the state of Scotland’s finances and the true nature of its starting deficit has been the cornerstone of the unionist argument. In recent years Government Expenditure and Revenue Scotland (Gers) figures have been gloomy reading for nationalists, suggesting that a starting deficit could be as much as £15bn. These numbers, though, are guesstimates that pay little heed to the exceptional needs and different spending priorities of an independent Scotland. They were established by a Tory government in 1992 for the specific purpose of showing Scotland’s finances in a bad light and cheerfully ignore that the fabled black hole in Scotland’s finances is the ultimate responsibility of a UK government, which still exerts the lion’s share of fiscal control.

Last week, the respected tax specialist Richard Murphy produced a detailed and articulate takedown of Gers. He said that they were “failing to collect the data that Scotland needs” and that they were “providing what may be some pretty poor estimates in their place”. Even so, whatever comfort has been gained by unionists in the past in dire economic forecasts is weakened when the full Brexit apocalypse becomes clear.

Yet even without all of this – Brexit; a dictatorial prime minister; the Ukip-style antipathy to foreign nationals – another referendum was always inevitable. The SNP is set fair to rule in Scotland for another generation, but crucially so too is an increasingly hard and reactionary rightwing government in England. The prospect of another 15 years of one-sided austerity, anti-trade unionism, anti-immigration, tax breaks for the super-rich tax evaders was always going to result in another referendum.

This time, though, the SNP believe that a Yes movement, which has retained its 45% support base, can win. They will be up against a weakened Better Together movement with no credible leader in Scotland and a prime minister trying to fight a war on two fronts. The fight is seeping out of some Scottish unionists, who now believe they have been misled by the UK government on Brexit and who are appalled that the UK is now following an agenda set by Nigel Farage, Boris Johnson, David Davis and Liam Fox and their desire to build another British empire.

Kevin McKenna has been nominated in this year’s Scottish Press Awards in the category of columnist of the year