If the union is to survive, the left needs to shape its own bold and hopeful patriotism

Without the saltire – Scotland’s national flag – and its distinctive white cross and blue backing, there can be no union jack. Without Scotland, singing Rule, Britannia! while waving the flag becomes an impossibility. At the cabinet meeting of 21 July, Michael Gove, brought up in Aberdeen, passionately spelled out the mortal threat posed by Scottish independence to the survival of the government – and Toryism. It would lose not just the union, but all the symbols of Britain that went with it. Its legitimacy would be shredded.

Yet last week Scotland’s first minister, Nicola Sturgeon, announced the Scottish government would introduce a second referendum bill in the coming parliamentary session. Her timing – she’s as cunning a politician as Boris Johnson is stupidly reckless – was impeccable. She calculates that the Johnson cabal in No 10 is heading for a rupture with the EU, whether no deal or a fig leaf deal, which will form the backdrop to the Scottish election campaign next spring. Aiming to capitalise on polls showing a firm 55% majority now in favour of independence, she will argue that Scottish voters must give the SNP the mandate to insist on a second referendum. An independent Scotland’s first act will be to apply to join the EU.

The unionist parties in Scotland are in disarray. There are potent arguments to be made: about the economic non-viability of an independent Scotland, about breaking the ties of love and kinship built up over 300 years and the emotional value of the union, about dislocation many more times toxic than Brexit, about the essentially regressive, poisonous nature of any nationalism. But these fall on increasingly deaf ears.

Britain, in apparent permanent thrall to the little Englanders and incompetent careerists who constitute today’s Tory party, is unloved and alien. Let’s cut the knot and aim to be Denmark within the EU is the Scottish solution. It will be difficult and damaging for a time, but at least it’s a national project of which to be proud.

What is Britain’s national project to counter this and about which we can all as citizens feel proud? What would give the unionist parties in Scotland something with which to fight next spring? Some English opinion, growing on the right of the Tory party, thinks England should let Scotland go as Johnson has let go of Northern Ireland, allowing it to stay, de facto, in the EU single market and customs union. Irish reunification is thus a growing likelihood. England will become a shrunken Tory kingdom. Gove is correct - this is not national success.

With the Scottish Lib Dems out of the game and Scottish Tories trapped in Brexit and Englishness, the Labour party finds itself alone in having the potential capacity to hold the union together. Poor Richard Leonard, the party’s leader in Scotland, is under intense pressure to resign, lacking both charisma and any effective message. But no successor will fare much better unless the wider party gives them something compelling to say that gets beyond homilies about a productive economy and social justice. The SNP does that well. Scotland foretells the arrival of the biggest politics of all: the battle for the mind and soul of a country.

Here, Keir Starmer is beginning to lay the foundations. He did not fall into the trap set by the right over the confected argument over the Last Night of the Proms: patriotism, he said, was fine by him. The components of this big politics are becoming clearer: a combination of a vigorous contemporary patriotism, a new British federal constitutional settlement and a commitment to rejoin the EU validated by a national referendum. Only thus can the SNP be challenged.

Labour Together’s otherwise tough, clear-eyed review of its election defeat had one gap, underlined by the Democrats’ attack on Donald Trump over the last two days, fuelled by the reported way he calls fallen soldiers “suckers” and “losers”. In the US, as in Britain, there is huge latent respect for those who serve their country, perhaps especially in the poorer US states and places such as former “red wall” seats from where much of the armed services are recruited. Much of Trump’s base believes that military service must be valued. So does a crucial part of Labour’s base.

Related: Nicola Sturgeon vows to set out independence vote plans by next spring

One of Scotland’s most emblematic, loved and stirring events is the annual Edinburgh military tattoo. Pipes, kilts and battle honours testify to the crucial part Scotland has always played in the British armed services and how tight are the ties that bind. Scottish Labour needs to own events like these, alongside the Scottish BBC, the British Open at St Andrews and whatever symbol of union comes to hand, even Balmoral. Simultaneously, it has to offer a federal constitutional settlement offering Scotland entrenched autonomy. And it must repudiate Brexit: the SNP cannot be gifted the pro-EU position. Britain’s national project is as a federal country within an EU that strengthens Britain’s hard and soft power and of which Scotland is an essential part. The union jack and the European flag go hand in hand.

Over my career, it has been a privilege to know the great generation of now dead Scottish Labour politicians – John Smith, Donald Dewar, Robin Cook. They would all have gone for a strategy of this type. This is as big as politics gets – holding a great country together. It is beyond Johnson and the Brexit Tory party. Starmer and his party have become the thin red line. If they succeed, the prize is huge: not just sustaining a united Britain within the EU, but becoming Britain’s natural, trusted party of government. Gove sees the risk for the Tories. Does Starmer see the opportunity for Labour?

• Will Hutton is an Observer columnist