Scottish voters may have lit the fuse for a new UK constitutional crisis but this is a confrontation with a very slow burn.

The Scottish elections have returned a parliamentary majority for a second independence referendum and separatists will now claim a mandate to demand a vote — a claim Boris Johnson is refusing to accept.

In a system which makes an outright victory very difficult to secure, the Scottish National party scored an emphatic win but fell just short of a parliamentary majority, a point which will be seized on by Tories. But with the Scottish Greens also supporting independence, separatists have the numbers in Holyrood, the Scottish parliament, to back a second referendum.

Yet there is likely to be a long phoney war before any such vote takes place. Westminster has the final say on whether to grant a legal referendum and Johnson has made it clear he will refuse to agree to one. The UK prime minister will couch his refusal not in the language of absolute obstruction but in the argument that now is not the time. His line that Scotland, like the rest of the UK, must not be distracted while it is still recovering from the pandemic will carry weight with voters, which is why the SNP’s leader and returned first minister, Nicola Sturgeon, has made the same argument. But unlike Johnson she sees delay as minimal and will soon seek the powers to hold a referendum, setting up a constitutional clash which may well end up in the UK’s Supreme Court.

The Tory strategy is fairly clear. Stonewall for as long as possible, play up the benefits of the Union and channel funds north of the border. Brexit, which Scotland rejected by two to one, has powered separatist sentiment and has added a percentage of union-backing remain voters to the independence camp.

That Scottish independence is again a live issue just seven years after the last referendum is a direct consequence of Brexit, which makes it all the more crucial to Johnson that he not preside over the disintegration of the UK. His hope will be that delay helps the Brexit wounds heal enough for those voters to switch back to the unionist camp.

While the Holyrood arithmetic is undeniable, the lack of an outright SNP majority helps Johnson’s strategy. But while Tories insist they will not accede to another referendum, privately many accept they cannot indefinitely defy a majority of Scottish voters and that to be seen to be doing so may increase the separatist vote. Ultimately, unless the SNP tide recedes the moral case for another vote will eventually be irresistible. The union has to exist by consent.

But delay also offers challenges for Sturgeon since, in defiance of her own hardliners, she does not want to hold an illegal referendum which, by conjuring up images of Catalonia, could hurt an independent Scotland’s prospects of EU membership. To that end she will be shedding few tears over the failure of Alex Salmond’s breakaway party Alba to win a seat. Her challenge is to keep the pot simmering without letting it boil over. The Tories’ hope is that their delaying tactics will force her to miscalculate.

Even so, obstructionism will suit Sturgeon. After a long run of opinion poll leads for independence, the gap has now closed and the polls are currently too tight for her to be confident of victory. A year or two of London obduracy — of what she will depict as England and Johnson ignoring the Scottish people — may help her whip up support.

She will seek ways to magnify the grievance against London’s obstruction, probably by legislating for a referendum and defying London to challenge this in the courts. By contrast Johnson, while refusing a vote, will want to seem emollient, conciliatory and visibly seek to involve Scotland (and Wales) in UK-wide decisions. On Saturday he invited the re-elected first ministers of both countries to a summit to discuss the challenges ahead.

Sturgeon’s primary strategic success through the pandemic was projecting an image of confident leadership, which would reassure wavering Scots that it has rulers who can cope in a crisis. One can argue over the reality of Scotland’s performance but it is unarguable that she emerged enhanced from the crisis and she remains the SNP’s best weapon.

The key question for Tories is when and if they have to accept a second vote and what tactics they would then deploy. They do not need to convert diehard separatists, just win back a sliver of waverers. These are the people Johnson must hope to win back, but they are also among those least susceptible to his charms since they blame him for Brexit.

Johnson will hold out against a referendum as long as possible — the best way for him to win this fight is to avoid it altogether. But if he is forced to agree to a new poll, there are three main cards his government can play. It can and will use central government funding to show the value of the union. It may offer even more devolved powers, though this will never be enough to satisfy nationalists. And finally, it can demand a full and detailed programme on how independence would work, in advance of the vote so they can then attempt to pick holes in it. Key questions would be how Scotland can afford to be independent, given the collapse of oil revenues, what the currency would be and how it would manage a hard border with England if it rejoins the EU.

Of course, Brexiters know better than anyone that such practical questions can be trumped by nationalist sentiment. It is an irony that any future contest will invert the Brexit contest with the SNP making the emotional, nationalist appeal, and the Tories arguing on economic grounds.

But this is for the future. The Scottish election heralds a new conflict over the future of the UK but there will be a lengthy bout of shadow boxing before we get close to an end game.

Letter in response to this column:

Scotland aims to be the phoenix from Brexit’s ashes / From Jackie Kemp, Edinburgh, UK