Every time I cross the border, that unmarked line above the Tweed seems more significant. Of course it was always there – “This is the night mail, crossing the border” ran Auden’s poem – but right now everything in Scotland feels electrified with political meaning. Including the East Coast line: it’s a reminder of Cameron’s dogmatic dash to sell off this fine public sector money-maker before the election. Here’s yet another example of the contention that London has lurched to the right, making inevitable the sundering of social democratic Scotland away from Britain.

Exactly a month to the referendum, the polls show yes inching closer, though still far behind. The Edinburgh air is saltire blue with politics (though that may not be typical of Oban or Easterhouse). Yes/no seems to touch every element of life, ideas, friends, foes and visions of the good society. What a world away from the sour disengagement south of the border. During last weekend’s vibrant annual festival of politics inside the Scottish parliament at Holyrood, I found myself – a stray English participant – forced to think harder about questions of identity. What is it exactly that we identify with?

Absurd London unionists (not the same as the no side in Scotland) warned on the Times’s front page yesterday that Scotland may lose the royal family. Goodness knows why the Scots want the royals, but that’s plainly a nonsense. If she can be Queen of Tuvalu she can probably continue as laird of Balmoral and Windsor.

Other tintacks thrown in the road have been as unconvincing. The pound? Yes, of course a deal would have to be struck. Who knows, Scotland might join the euro some day or create its own currency: it has a positive balance of trade, while the rest of Britain doesn’t. The same goes for nonsense about pensions and the uncertain oil estimates.

The Tories at Westminster have been suspiciously unhelpful. Few things illustrate better how small-minded the modern Tory party has become than its petty response to the Scotland question from those such as Boris Johnson, sabotaging the devo-max offer: “For no reason we are promising the Scots more tax-raising powers. There’s no need to do it.” John Redwood threatens to downgrade Scottish MPs. Nasty, too, was the article by an Economist editor in the Sunday Times calling them whingers who deserve “the tap turned off” if they vote yes, or to “shut up” if they vote no. These neo-liberals simply can’t understand collective aspiration or the force of identity politics. Odder still for Tories, they seem unconcerned at what would be left of British pretensions in the wider world if the Scots did vote to go.

The first question is whether Scotland could hack it alone, and the answer – though Alistair Darling could not quite squeeze it out during the famous debate – is of course yes, though it might hurt. Among the most compelling yes voices is the group Common Weal. Its Robin McAlpine paints a vision of escape from the dark world of Cameron’s atomised, state-shredding, welfare-destroying society. If Scotland distributed earnings as fairly as Norway, the poorest would be on £25k and everyone would be better off, with the Holyrood treasury gaining £4bn. He talks of the awakening of unpolitical people to the possibilities of a better future – not parties but communities enlivened to take action for themselves, to thrive whichever way the vote goes, quoting “a granny” who said that from now on “I’m no going back to my sofa!”

That’s inspiring, but it is not the whole story. Though tribally anti-Tory, there’s no great sign that Scotland is more than a little to the left of Britain. Inequality is as wide, poverty as deep, and it would take an enormous shift in income distribution to match Norway. That means huge predistribution of pay and redistribution of tax and benefits. What has Scotland done with its powers so far? Neither Labour nor the SNP used any of the 3p extra they could raise in income tax: easier to do it next year with new rules, but no party dares talk of raising tax. Instead, Salmond promises a beggar-my-neighbour cut in corporation tax in a deadly race to the bottom, letting business pay even less.

Nor have the poor come first. The SNP opposed tuition fees and introduced free care and prescriptions, but all those were free anyway for the poor, so the sizeable funds spent went to those on middle incomes and above. In other words, it looks as if Scots politicians calculate their voters are not entirely different from the rest of Britain.

But the second question is whether the yes voters who have written off Westminster politics are right. And the answer to that is no. I strongly believe social democrats are better together, confronting a common enemy – the forces of social injustice and social neglect – on both sides of the border, and convincing voters that more equality is better for all. Cameron’s party has not won an election for 22 years, and I doubt they’ll win next time either. It’s no time to give up on a British social democratic future.

As for Britishness, it’s a rum thing. I took down my old copy of the National Song Book. My generation in our school tunics used to sing Charlie is My Darling and the Skye Boat Song along with Men of Harlech and The Harp that Once Through Tara’s Halls. We sang these sad calls for freedom from the four corners of Britain with equal gusto: I wish children still knew the old songs. Those sentiments are universal.

Alex Salmond was in Arbroath yesterday, delivering his own declaration, steeped in the words from the days of Robert the Bruce – fighting not for glory but “for liberty alone which no honest man gives up but with life itself”. That’s what fighters the world over say, whatever their cause is, good or bad, in Iraq, Syria, Ukraine, Gaza, Israel, Sudan, Libya or Afghanistan. But this year’s first world war anniversary has been a reminder of how far we’ve come in Europe. Scots are stronger supporters of the EU than the English. A community of people bound by broad values is far more inspiring to me than small groups of people dividing up particular pieces of turf. What binds me is less the land I accidentally share with David Cameron and Nigel Farage, but ideas I share with other social democrats anywhere. Being in Scotland now as progressive ideas light up the political scene is another reminder that borders don’t define identities. The song I would sing to Scotland now is Jacques Brel’s mournful Ne Me Quitte Pas.