AN early autumn morning in Edinburgh, sometime in the mid-1990s. Two men are walking together through the Meadows. The sun has cast a dull light across the tree-lined paths. They turn up Middle Meadow Walk, passing Edinburgh University’s George Square campus on one side and the crumbling old Royal Infirmary building on the other. As they approach the junction at Teviot Place, their conversation intensifies. They no longer notice the students, the coffee-sellers or the cyclists. They are speaking, in fluent Italian, about Marxist philosopher Antonio Gramsci. One of the men, dressed in a distinctive tweed hat and cardigan, is Hamish Henderson, the celebrated Scots poet and folklorist. The other, less stylishly attired in a plain shirt and suit jacket, is Tom Nairn, the most influential Scottish political thinker of his generation.

You can see them, can’t you? Two silhouettes in the sunlight. Henderson died in 2002, aged 82, an icon of Scotland’s cultural left. But Nairn is still very much with us, and although, at 84, the years are beginning to pile up on him, he remains as perceptive and self-deprecating as ever.

“Hamish was my old neighbour along the road overlooking the Meadows,” he tells me when we meet at his small, semi-detached home on a quiet residential estate in Livingston. “He had come into contact with Italian culture a long time before I did.

“It wasn’t just pretence or showing off that we spoke in Italian. That’s just how we’d learned [Gramsci], and once you learn it in one tongue it becomes easier to carry on speaking in that tongue.”

More than anyone else, Tom Nairn has shaped how we think about the United Kingdom and its creaking constitutional architecture. He is the intellectual godfather of modern Scottish nationalism.

“The perception that Great Britain was a multinational state and not a united nation has never quite been lost over the centuries,” the journalist Neal Ascherson, one of Nairn’s oldest and closest friends, wrote in 2000. “But it was [Tom] who almost single-handedly hammered this truth into the skull of British intellectuals and campaigners until it became – as it is today – practically uncontested by the political class.”

Nairn made his name in the 1970s with his book, The Break-Up Of Britain. It was a savage attack on the whole edifice of British power, and it advanced the bold claim that Scotland and England were heading for imminent divorce. Westminster is “fossilised,” it argued. The economy is locked in a spiral of crisis and decline. The Celtic peripheries are straining for more autonomy. The Union is finished.

Some 40 years on, Nairn – who is retired now, and rarely writes any more – stands by his prediction, although he admits that the disintegration of the UK has taken longer than he initially anticipated. “It’s as hopeless as it ever was,” he says. “But it’s being prolonged because no-one can think of an alternative for the 80 per cent majority, which is the English, God bless them.”

We are sitting in Nairn’s front room. Large patio windows face on to a neat stone-work garden. I’ve been here before. In the summer of 2014, when I was co-editing a collection of Nairn’s essays – Old Nations, Auld Enemies, New Times – I was invited round for lunch. I was with Nairn, too, the last time he spoke in public, at the book’s launch event a few months later, on a humid September night three days before the independence referendum.

That feels like a lifetime ago. Nairn hasn’t changed much since then – in fact, he looks exactly the same, with his red woollen sweater and white thinning hair – but everything else has. The Labour Party is imploding; Britain stands ready to ditch its membership of the EU; and the SNP is preparing the ground for a second, decisive crack at independence.

Nairn thinks another referendum is both inevitable and necessary. “I personally see no alternative to it, with or without support from south of the Border. We can only do our own thing and cope with the result.”

But he believes the real challenge will come after a Yes vote, when Scots have to work out what sovereignty means for a small country in the 21st century.

“Everything has been called into question,” he says. “The world of old-fashioned nation-states has disappeared and some substitute has to be invented.

“I had a discussion recently with representatives from Plaid Cymru in Wales, and down there it’s known as ‘kilt-streaming’ – meaning ‘follow the Scottish lead’.

“But alas, you ask what the lead is, and the fog once again descends. In situations like this, one has to fall back on what’s there, on what has been bequeathed by relatively recent history, which is by definition inadequate.”

Nairn isn’t a natural conversationalist. He’s not fond of small talk. But he is patient and accommodating. He speaks slowly and deliberatively, in a deep, resonant voice, without any of the fastidiousness you might expect from someone of his global academic standing. Ahead of our meeting, I contacted a number of his friends and former colleagues. All of them, without fail, described him in the most admiring terms.

He is an “extraordinarily fine being, courageous and selfless as very few of us are,” Perry Anderson, the UCLA professor and London Review of Books essayist, told me via email from Los Angeles.

“What can I add that is not already known?” the Oxford-based writer Anthony Barnett said. “Tom is very rooted. He relishes regular life. He is generous and open-minded. There is no meanness, canniness, grasping, nothing Calvinist about him. This may even be a deliberate refusal of all the caricatures of Scottishness except for the democratic intellect, which he has profoundly. [He has a] quite exceptional steady capacity for judgement not f****d-up by calculation.”

Nairn’s professional trajectory has not been linear. In 1968, he lost his job as a sociology lecturer at Hornsey College of Art in London for supporting a student strike. He has spent long stretches of time abroad, at the University of Pisa in Italy, the Transnational Institute in Amsterdam, and the Royal Institute of Technology in Melbourne, Australia. In 1995, alongside the sociologist David McCrone, he established a masters course in nationalism studies at Edinburgh University, but he left after four years. Astonishingly, he has never held a permanent academic post in Scotland, which explains why he has so frequently found himself living and working in other countries.

I wonder if his experiences abroad altered or clarified his thinking in any way. “It was mainly being out of not just Scotland but Great Britain, on the other side of the world, and then coming back into the fog, from Melbourne, Victoria State, in Australia, and confronting the old problems,” he says. “But I didn’t return with any easy or glib answer to those problems. This is cold comfort for those who would like a more viable formula to present itself, but it’s not going to.”

Scotland, nationalism and the left have been the major, overlapping themes of Nairn’s life. They run like a thread, with varying points of emphasis, through almost everything he’s written.

He was born in Freuchie, a small town at the foot of the Lomond hills in Fife, in 1932. His father was a headmaster at a local school; his mother stayed at home. He studied philosophy in Edinburgh before moving to Oxford, where he was briefly taught by the novelist Iris Murdoch. After that he joined the New Left Review, the UK’s leading socialist journal, in London. Scotland was not one of his initial concerns.

“I met Tom in 1968 during the Hornsey Art College strike and occupation,” the author Tariq Ali recalls. “His interests then were Italy and Gramsci, Marxism and the Labour Party. The fact that he was Scottish meant little to those who knew him at the time. That came a bit later.”

Nairn returned to Scotland in the 1970s as the debate over independence was gathering pace. He had been scathing about the SNP, at one stage branding them, only half-jokingly, “a junta of corporal-punishers and Kirk-going cheese-parers”. But his attitude changed as a new generation of leftwing activists emerged within the party. He has never shown much interest in public policy. He maps broad historical trends. Just as his views on Scotland evolved, so too did his relationship with Marxism. The end of the Soviet Union was an important moment. It made him less prescriptive; less confident that class was society’s key galvanising dynamic.

“Marxism was part of the old world,” he says. “The idea that social class would be the main guide, provide the leadership, the way forward; it didn’t, it couldn’t, and the collapse of the USSR has shown this, unmistakably.”

Does he still consider himself part of the left? “I do in the sense of not being part of the neoliberal tide or its side-currents. I suppose that was one of the benefits of old-fashioned Marxism: it inoculated us against other enthusiasms, replacement philosophies and ideologies.”

Nairn has his critics. He’s not very popular with unionists, for one thing. But it’s hard to deny the force of his analysis. When I was editing Old Nations in 2014, I was repeatedly struck by how prescient his work has been.

Years ago, he issued a stark warning: without a “radical, left-directed breakthrough” in English politics, the UK’s next constitutional crisis will be accompanied by a conservative backlash. After the ugliness of June’s Brexit vote – and with Theresa May’s Tory Government launching a fresh crack-down on foreign-born workers – there is a feeling that Britain is in the grip of a right-wing surge.

Nairn doesn’t quite see it like that. He views Brexit as symptomatic of a deeper struggle over England’s place in the world, its national purpose and identity.

“England has always been a problem in that sense,” he says. “It has been too big for its boots since before the day it was born, and it’s now faced with the problem of becoming just another nation, and assuming some kind of local, limited identity which ends at the Scots Dyke, among other places, and they don’t know what to do about it.

“Whole generations, one generation after another, have been brought up to believe that externally directed growth – ‘The Empire!’ – was always the answer. Now one engine [of growth] has to be replaced by another.”

Is the rise of Labour leader Jeremy Corbyn a belated attempt by the English left to get its act together?

“Oh undoubtedly, but Corbyn has only posed the question in order to not have an answer. And how can there be an answer without a more decided means of English identity? As soon as you see this you’re in trouble all over again … So it looks like Corbynism is just another act of floundering in circles.”

Floundering in circles. Without Nairn, that’s what Scottish nationalism would be doing. Ironically, although he is set to receive an honorary degree from Edinburgh University next month, he has never really embraced his status as Scotland’s leading public thinker, and in some ways Scotland has never really embraced him.

“There should have been a Nairn Institute for Political Thought at a Scottish university decades ago,” the constitutional campaigner and Princeton academic Will Storrar says.

“Instead we have had what I seem to remember Tom once called Hugh MacDiarmid: a wandering Moses McOmnibus, a one man peregrinating genius.

“His best thought on Scotland has yet to come, and we shall spend yet more decades drawing on his brilliance.”

I agree. Nairn may be in his twilight, but the national conversation he started, the national journey he so profoundly shaped in his work – that long, wandering, multiform walk across the Meadows, Edinburgh, Scotland and beyond – is far from over.