FEW books about politics stand the test of time like Tom Nairn’s The Break-up of Britain.

Next year will see its 40th anniversary. Originally published during the Queen’s Jubilee of 1977, the book offered a blistering counter-blast to the official commemorations – and self-congratulation – of political and media elites who used the occasion to reflect on the wonders of the British way of doing things.

The UK has undergone dramatic change since then. Superficially in form and appearance it still looks similar. But that belies realities. Economic and social changes have produced a bitterly divided country of self-obsessed, triumphalist winners and millions of losers.

There has been devolution to Scotland, Wales and Northern Ireland, as well as restoration of London governance, but the political centre hasn’t reformed. Instead, it has got worse, with power more centralised in the prime minister and no process of democratisation.

Nairn’s original thesis is so far reaching and prescient that it has often been misunderstood and misrepresented. The opening words of Break-up State: “Only a few years ago, the break-up of Britain was almost inconceivable,” but this was changing then, and is now mainstream thought.

What were the main elements of Nairn’s arguments and why do they matter today? First, Nairn made the case that we still had an unreformed British state, one that had never fully democratised, but still had relics and practices from the feudal age.

It never experienced a fully fledged bourgeois revolution, unlike most of the states of western Europe — thus allowing an elitist culture and continuation of such undemocratic practices and institutions as the Crown Powers and House of Lords.

Second, this state of affairs didn’t just affect conservative, reactionary opinion, but liberals and left-wingers too. Thus, the Liberal and Labour Parties bought into this, and saw it as fair and the British state as ‘neutral’. Labour in particular, as the party of the bigger state, saw it uncritically as a vehicle for delivering progressive change.

Third, Nairn foresaw in the 1970s how Europe and European integration would challenge this unreconstructed idea of Britain. It presented a different idea of the state, sovereignty and society — one where rights were more codified, and the economy based more on partnership and collaboration. This struck at the heart of the Tory-Labour idea of where power emanated from: The sovereignty of parliament, providing a check on the untrammelled powers of government.

Finally, he drew this together into an understanding of how the component parts of the UK were pulling apart. Nairn had before and has since written extensively about Scotland, but in Break-up he devoted equal time to England, Wales and Northern Ireland. The last two were emerging as distinctive and increasingly autonomous nations – pointing to the fragmentation and ultimate end of British politics.

Perhaps his most penetrating analysis came with relation to England. Part of the Great British bargain had been the submergence of its biggest component, England, in the UK. The failure to make a more equal country during the rule of successive Labour governments, combined with Europe and the dynamics of globalisation, would lead to a new English dimension and more pronounced regional voices within that.

This world has come about. Scotland, Wales and Northern Ireland sit in a very different political space from Westminster. The entire Eurosceptic debate has been driven by English concerns and anxieties, and yearning for a world that has passed away. Ukip and Nigel Farage have given voice to a sense of loss and nostalgia.

Scotland’s role in this was central. Its constitutional debates offered a chance to resist the over-reach of Westminster and parliamentary sovereignty, and portray a different kind of politics. This analysis didn’t shy from the conservative and complacent attitudes within Scotland’s elites and the Labour and Nationalist traditions. But Nairn believed that the re-emergence of self-government and a modern Scottish nationalist tradition gave Scotland the opportunity to escape the fossilised British state while also showing the limits of “left proletarian internationalism”.

The Break-up of Britain is forty years old next year – as Nairn turns 85. Its penetrating and prophetic analysis has in many respects become the Britain of today, but like many sages before their time, Nairn is less hailed and acknowledged outside of select left-wing, Scottish-nationalist and academic circles than his reputation deserves.

What Nairn did all these years ago was map out the contours and drivers of what in effect is the decline of the very idea of Britain, its formal structures and the emergence of a post-British sensibility among the people and nations of these isles.

Today’s Britain is one that the Westminster political classes struggle to understand and describe, one that has unleashed an economic and social revolution that has turned people’s lives upside down, using the undemocratic practices of the British state to impose changes based on minority popular support.

As the British state declines in respect and authority, it is worth remembering that over the last forty years it had several opportunities to change and reform, to fully democratise and enter the modern age, and embrace the idea of Europe. At every possible moment it has failed to do so.

Now, when politicians such as Gordon Brown propose a ‘sort of federal Britain’, or confederal arrangements as he did last week, we have to conclude that this is too little, too late.

Nairn’s Break-up argument wasn’t completely deterministic, and even he never foresaw the scale of decline, denial and imperial grandeur that characterised the worst excesses of Thatcherism and Blairism. But he got the underlying dynamics spot on – and recognised the failure of successive radicals past and present to challenge the British state.

Today we live in Nairn’s Disunited Kingdom, and if Westminster politicians don’t know this, and cannot acknowledge it, then Scottish ones should and can. Scotland, even more than the rest of the UK, not only experiences these crises and decline on a daily basis, but even more than the rest of the UK has the opportunity to do something fundamental about it.

Gerry Hassan is author of Scotland the Bold: How Our Nation Changed and Why There is No Way Back, just published by Freight Books, £9.99.