A year ago today (Friday), Brits went to sleep not knowing if the country would still be intact when they woke up. The referendum on Scottish independence had ended in a surge of support for the separatists, and their victory seemed not only possible but likely. The partition of Britain, an idea that had once seemed too daft to take seriously, very nearly happened. Just under 45 per cent of Scots voted for it, raising fundamental questions about our national cohesion. It's an old argument.
"You talked of Scotland as a lost cause," John Steinbeck once wrote to a friend; "That is not true. Scotland is an unwon cause." That's certainly how Nicola Sturgeon sees it. The First Minister now talks about when, rather than whether, a second referendum will take place. We can expect one in the manifesto for next year's Holyrood election, which is almost certain to give her a commanding majority. Three factors work in her favour: her rock star popularity, her command of a government machine able to fight for independence every day, and a UK Government that can't bring itself to fight back.
For unionists, there was no great victory last year. The celebration in No 10 demonstrated the lack of understanding which led to this mess in the first place. Separation would have been a calamity but the closeness of the result was still a disaster; all the more because the "No" side had relied upon relentlessly negative arguments. To Andrew Cooper, formerly David Cameron's chief strategist, this was the only way to win. Later, he said the only criticism he would allow of his campaign was that it was not negative enough. It was a poison, which had the desired effect against the enemy. But it has swirled around the Scottish political bloodstream ever since.
It led to the implosion of the Scottish Labour Party, the quadrupling of the SNP's membership and the party taking 56 of Scotland's 59 seats at the general election. Using old-style politics - street campaigning and village hall meetings - it has assembled something that often looks closer to a religion than a political movement. And Sturgeon has brilliantly kept the debate on her preferred territory: endless squabbles about constitutional reform. When speaking about Scotland today, David Cameron is expected to refer to "tabling an amendment to the Scotland Bill", still dancing to a nationalist tune.
Sturgeon's seemingly unassailable position is all the more baffling when you consider the mess that her party has made of the powers it already wields. The SNP has governed public services in Scotland since 2007, so it is easy to test its central theory: that "home rule" is better rule. If this were true, we would see Scottish students pulling ahead of English ones; hospital waiting times crashing down and exciting and innovative methods of policing. Instead, a very different picture presents itself for those with an eye to see it.
The steady exam improvement in England has seen no equivalent in Scotland, which is now the worst place in Britain to be poor and bright. Next month, almost one in five English students from poor backgrounds will go to university - twice the level of poor Scots. Lucy Hunter Blackburn, a former civil servant who crunched the numbers in an Edinburgh University study, puts it starkly. The SNP's abolition of tuition fees helps rich families, she says, and grants for poor students are lower. So the SNP "is actively reinforcing inherited inequalities in wealth. It's that simple."
The SNP's great policing experiment - merging eight constabularies into one nationwide force - has also become a case study in what not to do. The promised cost savings have not materialised, the huge force struggles with basic communication and is under fire for bungled responses to emergencies. In July, a man was found dead inside his car near Bannockburn three days after the crash was first reported. His girlfriend was unconscious next to him. She died later. Sir Stephen House, chief constable of two-year-old Police Scotland, recently announced his resignation.
If Theresa May's flagship police reform had gone so badly, she would be an ex-Home Secretary. But things are different in Scotland. The SNP is adept at changing the topic of conversation to one it prefers and dodging the scrutiny it deserves. It likes to hold debates over issues where it has no authority. On Tuesday, MSPs discussed the refugee crisis and voted to "recognise the severity" of the situation as if this would do any good. About pounds 1 billion is being spent helping Syrians by the UK overseas aid department, which has hundreds of staff in East Kilbride. If the SNP wants an example of Scots making a difference to those most in need, it need look no further.
So there is a scrutiny gap, which Mr Cameron's Government can help fill. As Prime Minister of the United Kingdom, it ought to concern him that educational opportunity is being denied to bright Scottish teenagers simply because they lack the money. But there is good news too. Poverty in Scotland is falling, contrary to the SNP's predictions. It is also one of the very few countries in Europe to enjoy record employment; who would argue that this is unconnected to its being part of the UK and its jobs miracle? Mr Cameron could trumpet these successes.
All party leaders are likely to speak about Scotland on today's anniversary, but it would have been nice if the Prime Minister's remarks were made up there. Such symbols matter - as the Scottish Tory leader, Ruth Davidson, pointed out recently. Those who care about Britain, she said, should "wake up" and recognise that the battle for Britain is being fought. It's possible that her remarks were aimed at her Cabinet colleagues in Westminster, most of whom have relegated Scotland to the very back of their minds.
The Conservatives' great mistake, last time, was to think that the union was safe because the SNP's proposal was too implausible. Today, support for independence stands at around 50 per cent; only one in five Scots is confident that the Union will survive the next few decades.
One feels for the Prime Minister: he has enough battles to fight. But the battle for Scotland is still very much one of them.