Boris Johnson knows better than most the power of an independence movement in full flow. But now he finds himself behind the very barricades he once so joyously stormed. The news from Scotland is all bad for the UK prime minister as he faces a buoyant separatist movement and the horror that he may be remembered as the man who lost the Union.

Officially, the government’s position is that there will be no new vote on independence even if, as expected, the Scottish National party sweeps this year’s Holyrood parliamentary elections.

But few insiders believe this position can hold. “For people saying there will not be another referendum there’s a lot of activity going on,” says one of those close to Mr Johnson. A cabinet minister adds: “The time we are now spending and ministerial focus on the Union has changed massively.”

The pressure went up another notch last week when Nicola Sturgeon, Scotland’s first minister and SNP leader, said she would hold an unapproved advisory referendum if Westminster refuses a sanctioned vote. Even if unionists boycott a poll, it keeps the issue simmering.

Meanwhile, the UK government’s brightest brains are searching for a killer strategy. Some argue for giving more powers to Holyrood. Others tout a constitutional convention that will, conveniently, take up time. Many want more aggressive signalling of all the ways Scotland gains from the Union’s “broad shoulders” (Covid vaccine, anyone?), a point Mr Johnson will hammer home on a visit this week. Some ministers talk about devolving power closer to the Scottish people — code for bypassing Holyrood and pushing more funds and powers to local councils.

All have a ring of schemes dreamt up by clever policy wonks and they miss a fundamental point. Aside perhaps from giving the nations of the UK veto powers over UK-wide policy — anathema to English Conservatives — there is no cunning constitutional wheeze that saves the Union. In any case, the “more power over your future” card was played in the 2014 independence referendum and has been shot to pieces by Brexit, which Scotland opposed by nearly two to one.

If this fight is to be won, it will have to be won on the basics. An independence referendum comes down to one simple question: will life be better if you take control of your own affairs?

Mr Johnson is not wrong to delay the reckoning. Polling suggests England’s “imposition” of Brexit has tipped separatism into the majority position. But polls also show most Scots do not see an urgent need for another vote. Hence the plan to stonewall. Delay could buy time perhaps for a change of circumstances, an SNP descent into internal feuding or a Labour revival to draw votes from the nationalists. Amid a pandemic and its economic consequences, “now is not the time” remains a useful argument.

But as long as independence is the dividing line in Scottish politics (and the unionist vote is split between three parties), an SNP collapse may be wishful thinking. Delay also means the loss of older voters, who are more likely to favour the Union, while younger people lean heavily towards a breach.

In any case, it is not a viable long-term strategy. The SNP will use Westminster obduracy to their advantage and it knows no London government can indefinitely refuse to hold a new vote. “Something will turn up” is not a strategy; the Tories need a plan B.

There are two potential paths. The first is obvious. While unionists want to make a positive case, their strongest emotional card is fear. But Brexit saw “Project Fear” losing out to “Take Back Control” as nationalism trumped economics. Scots also see Brexit as a more ruinous economic policy than anything the SNP might propose and are drawn to the chance of rejoining the EU after independence.

Even so, Scotland’s economic prospects have declined with the collapse of North Sea Oil revenues. Furthermore, the UK’s Brexit terms would leave Scotland facing a hard border with England, its largest market. Tory Brexit campaigners believe the economic case can be made more effectively with fewer, simpler messages.

But this approach needs a concrete plan to contest, which leads to the other option. Since Westminster must sanction a new referendum, it is able to set the terms and can learn from Vote Leave’s key tactic of refusing to specify how Brexit would work, a move that robbed Remainers of attack lines.

The UK could agree to a vote but only once the SNP has brought forward a detailed programme for independence that includes such matters as its plan for the currency — how soon it would swap the pound for the euro; its future relationship with England; how it would enforce single-market rules on the English border; and even its proposals for funding the NHS or other public spending. The Scots would be forced to focus on real change and weigh the significant costs of rupture against the status quo.

There is no guarantee of success. Scots may be past the point of no return. But it would at least force an honest, realistic debate, matching up two futures and preventing the magical thinking that served the Brexiters so well.

It is a risk, but if the SNP maintains its grip, another vote cannot be dodged. Scotland cannot be held indefinitely against its will. The Union cannot be maintained by delay or constitutional tweaks. Ultimately, it can only be saved by winning the argument.