The UK’s Supreme Court has ruled Scotland cannot hold a second referendum on independence without the Westminster government's consent.

In their manifestos for the 2021 Holyrood elections, the SNP and Scottish Green Party both stated that their MSPs would push for such a vote. Between them, the two parties won 72 of 129 seats, a clear majority. They agreed to govern together, and proposed the referendum be held on 19 October 2023.

Rather than holding a referendum that unionists say is illegitimate and boycott, or that is banned by the courts halfway through the campaign, Scottish first minister Nicola Sturgeon presented a draft referendum bill to the country’s top legal official, Lord Advocate Dorothy Bain, and asked her to go to the Supreme Court for an opinion on whether it would be allowed.

Today, the court said no – affirming that constitutional matters are reserved for Westminster. Sovereignty in Britain doesn’t rise up from the people, it cascades down from the King-in-Parliament. Westminster gets to decide who gets to decide what, and Westminster has always been pretty clear that matters pertaining to the break up of Britain are firmly within its purview.

Scottish government’s lawyers had argued that referendums in Britain have always been consultative. A Yes vote for Scottish independence wouldn’t automatically seal a piece of legislation that was or wasn’t constitutionally viable, it would merely indicate the will of the Scottish people. The ramifications of that decision – that it would become very hard for Westminster to refuse independence – are matters of politics, not law.

But regardless of the court’s ruling, the issue of independence is not going away. Sturgeon has made clear that such a decision will mean she treats the next Westminster election as a de-facto referendum: if the SNP and Greens get more than half the Scottish vote, they’ll consider it a mandate for independence.

The question is, will anyone else?

Polling this summer showed that 39% of Scots think a majority for pro-independence parties in a Westminster election would amount to a mandate for independence – only 1% more than those who think it wouldn’t. This is far less than those who think a mandate would be provided by a Yes vote in a referendum agreed by both Westminster and Holyrood (63%) and in a referendum organised by Holyrood without Westminster’s agreement (47%).

Perhaps events between now and the next Westminster election, scheduled for 2024, will mean those figures will have shifted. Maybe the perceived incalcitrant attitudes of the British political and judicial systems will have pushed the undecideds off the fence. But perhaps they won’t.

Then there will be the reactions in Westminster. In 1989, the overwhelming majority of Scottish MPs – mostly Labour and Liberal Democrat – signed the Claim of Right, in which they proclaimed “the sovereign right of the Scottish people to determine the form of government best suited to their needs”.

Now the court has struck down that claim, will those parties speak out? Or have they repudiated their faith in the Scottish people? And how will both parties, and the Tories, respond if there is a pro-independence majority at the next election? Will they accept that mandate? What will the oft-touted ‘international community’ – a phrase that really means the EU, the US and, to some extent, China – say?

If anyone benefits from the chaos that is sure to follow the Supreme Court ruling against a referendum, it is likely to be those who oppose independence. For nearly a decade, unionists have worked hard to focus on process, to argue against another referendum rather than against independence, to do all they can to avoid having to make a clear case for the Westminster political system. I can’t say I blame them.

But there is a big risk for unionists in dragging the whole thing out. Among voters who have grown up with the Scottish parliament – those aged between 16 and 34 – almost three-quarters support independence. The survival of the union relies on the support of around two-thirds of the over-65s, for whom Holyrood feels like a new invention. The longer Westminster delays, the stronger the demographic pressure for independence will become.

But I’m getting ahead of myself. The courts in London have ruled that the people of Scotland cannot vote to grant ourselves a referendum on independence. The rules of the British state do not provide a mechanism through which Scotland can un-sign the 1707 Act of the Union.

For supporters of independence, that shouldn’t come as a surprise: much of the reason many of us aren’t fans of the British state is the centralised, top-down nature of it.

But the question now is not just how to persuade our fellow Scots of the case for independence, it’s also how to win the right to it.