On Thursday, Scotland will take a decision of seismic consequence for the 307-year-old union. Tempered and tested by the Industrial Revolution, the empire, the carnage of war, the birth of the welfare state, it is a union that has been strengthened by the mutual inventiveness and talents of complementary identities. It has been pluralistic, democratic, multicultural, tolerant (mostly), enlightened (for the most part), liberal. As political unions go, it has been a remarkably successful one.

But whatever the decision on Thursday, the result should act as a catalyst for change, a harbinger of constitutional shifts for the whole of Great Britain. The Scottish people set out on this journey alone – but they have unwittingly taken on board passengers from the rest of the union. When Gordon Brown – backed by the three Westminster party leaders – last week promised Scotland "nothing less than a modern form of home rule" if the vote is no, it signalled that the constitutional make-up of these islands is about to change irrevocably.

Ed Miliband goes further: writing for this paper today, he suggests that were he to become prime minister the union would undergo fundamental change. "Scotland's example will lead the way in changing the way we are governed in England too, with the devolution we need to local government from Cornwall to Cumbria." Few, if any, people were talking about devolved powers to Cumbria or Cornwall two weeks ago. It is a sign that, regardless of the outcome on Thursday, the first minister, Alex Salmond, has already won a significant victory.

The decision by the three main Westminster parties – spooked by a poll showing the yes campaign in the lead – to make significant promises of more devolved power revealed how remote they are from the political and cultural winds swirling in Scotland. Cameron, Miliband and Clegg had 18 months but they waited until the last 10 days to spell out just how profound devolution could be. It wasn't a terrific advertisement for how well the union is working.

The offer of devolved powers came alongside warnings about the alleged cataclysmic economic consequences if yes wins the day. Among the growing list of economic tremors they say are about to hit are rising food prices, fewer jobs, higher taxes, reduced postal services, weaker pensions, volatile currency, crashing property market, a flight of the banks, plunging oil revenues, and more besides.

The significant failing of the no campaign is that the arguments in favour of the union as a powerful unifying force which has mobilised a poetic and powerful sense of shared strengths and values have barely been voiced in this campaign. Instead, the no campaign's weapons of mass destruction have been almost universally economic, and punitively deployed.

This has been evident again in the force of corporate and financial power unleashed in the last two weeks. The threatened financial loss to voters may offer a sobering prospect (as our poll suggests) to those who are wavering. However, in making this the centrepiece of the attack on the yes campaign, it confirms for many Scottish voters that finance and money exert a powerful influence on the upper reaches of the body politic. But that political elite has failed to find ways to improve the life chances of many Britons over the last 20 years. There is more to the union than the value of sterling but the no campaign has had real difficulty in telling that story.

It is the yes campaign that has, sometimes shamelessly, gained ownership of the romance and the poetry. It has remained determinedly optimistic, insisting that membership of the European Union, Nato and even currency issues can be easily sorted. But the holes in the SNP position, sketched out in the white paper, Scotland's Future, have become increasingly clear.

Scotland, helped by North Sea oil and a funding mechanism gifted under the terms of devolution, is now among the wealthiest countries in the world but it also has the highest levels of inequality in western Europe. And here lies a conundrum. Salmond offers universal childcare, free prescriptions, no fees at university, free social care, higher pensions, an end to Trident, a challenge to the bedroom tax and a securely non-privatised welfare state, anchored firmly in the social solidarity of the 1945 welfare settlement. At the same time, he advocates "a light touch" on business, cutting public expenditure, opposing 50% as the top rate of tax, promoting deregulation, and competing with the Treasury to slash corporation tax. It is difficult to see how these competing visions can balance.

The yes campaign has failed to address the complexities, compromises and likely conflicts that independence will create. If the no campaign suffers from being overly punitive, the yes campaign promises too much. It is tempting to hear the siren call of self-determination and warm to the notion of a small, independent state making its way in the world. Tempting, but how realistic? As Fintan O'Toole wrote in the Glasgow Herald last week: "Freedom does not arrive just because you declare it. And if it ever does arrive, it is complicated, constrained and contested. Too much has happened to too many dreams of national liberation for any sensible citizen to believe in a great moment of transformation after which everything will be simpler, purer, better."

Supporters of independence could do worse than look across the water to see just how independent Ireland has fared over the last five years as the EU and the IMF have all but run that country's finances. Part of what is being heard on the doorsteps of Scotland is a fierce resistance to the status quo. The rest of the UK is not immune from these sentiments. Very large numbers of people in the rest of the UK feel equally strongly about entrenched injustice and complacent institutions and feel common cause with the Scots. This surge of disenchantment presents radical challenges to the union. But we should at least rejoice at the intense engagement with a different kind of politics that the referendum campaign has sparked.

In homes, pubs and clubs in Scotland, it's heartening to witness a revival of faith in exercising the hard-fought right to vote. The turnout on Thursday is predicted to be extraordinarily high. There are valuable lessons to be learned from this democratic renaissance. Many of those in the yes campaign are not "blood and soil" nationalists or fans of Alex Salmond. They are motivated by a conviction that the system itself has to change. Inequalities must be tackled; redistribution of resources made fairer, the common good reasserted. The same inequalities and resentments and desire for a new deal can easily be found south of the border.

As Will Hutton wrote in these pages last week, in explaining what was driving much of the enthusiasm for the yes campaign: "The big argument is that Scotland does not need to be permanently yoked to English Toryism's infatuation with a libertarianism that denies obligations to society and each other ... and is the author of the great 'cashing out' of the past 30 years. All our utilities, five million council houses, many of our great companies and swaths of real estate in our cities have been cashed out in the name of market forces, of being open for business and wealth generation. What has been created is predator capitalism, massive inequality and a society organised to benefit the top 1%."

But is a transition to a different sort of Scotland possible – or even preferable – without an end to the union? Gordon Brown has recently been reinvigorated as the father of British federalism. "Westminster's claim to undivided authority over the country? Dead and buried," he wrote recently. The upshot after a no vote, he argued, could be "a system of government as close to federalism as you can have in a nation where one part forms 85% of the population".

But this will not be an easy transition. As Andrew Rawnsley makes clear in these pages, the gifting of greater powers to Scotland will have serious political repercussions for the rest of the union. One senior cabinet member notes: "The slumbering beast of English grievance will wake up." A new political settlement in which a resilient Scotland plays a key part does offer the prospect, as Will Hutton noted, of a new awakening for the whole of the UK: "This has to be a recasting of the British state so that Scotland, Wales, Northern Ireland and all Britain's great cities and towns have the autonomy they need to create the societies and culture they want but within the protective umbrella of Great Britain. This would be the best of both worlds, and not just for Scotland."

The attempt to convince Scotland that this is the correct path has to start with a recognition of why many Scottish people are increasingly drawn toward self-determination. From 1945 to the 1970s, the working class benefited from "high Scotland" as the country flourished. Jobs, homes, education provided the fuel for the engine of social mobility. In 1979, one in three in the Scottish electorate voted Tory, sending 22 MPs to parliament. At the 1979 referendum on devolution, a third were in favour, a third stayed home and a third voted against. Then came the decline in manufacturing and heavy industry, rising unemployment and the introduction of the poll tax in 1987 in Scotland, ahead of the rest of the UK. Support for both main parties has plummeted as the numbers who felt disenfranchised grew. Brown argues that Scotland's loss of a million jobs has been due to globalisation. He argues that the union, reinforced, can fight the impacts of globalisation far more effectively than two countries each weakened domestically and internationally by the split.

Today, the poorest 30% in Scotland's population of 5.5 million receive only 14% of the national income. In 2012, the richest 100 in Scotland, according to Gerry Hassan in Caledonia Dreaming, had accumulated £21 billion in wealth. According to Oxfam, a child born in Lenzie, north Glasgow, lives 28 years longer than a child born in deprived Calton. It is a myth that Scotland has a special culture of egalitarianism – social divisions and exclusion are as real as in other parts of the United Kingdom. At the same time, the union has helped to raise the nation's standard of living (even as inequality has accelerated). According to figures quoted by Gordon Brown, it costs £1,725 per head for all pensioner benefits, but Scotland receives £1,805 per head from Westminster – a difference of £80 which will rise to £120 over the next two decades. The referendum, however, is also about something that it is difficult to price – namely exercising power in your own name. Even if that sort of power comes with new levels of responsibility.

As Fintan O'Toole wrote last week: "National freedom isn't another word for nothing left to lose. It's another word for no one left to blame – no one, that is, except yourself. If you make your own choices, you become responsible for their consequences. Patriotism is a rocket fuel that can get you out of the orbit of an older order but it burns up quickly and leaves you dependent on much more complex and subtle systems of guidance to get you through the lonely expanses of historical space."

Such tricky navigation requires leadership in all areas of government of a calibre that is hard to find. It requires global events running in a new country's favour and an electorate with the patience to accept that it takes decades to achieve proper representation and maturity to exercise power fairly.

Scotland, if it votes yes, will be a small state in a rapacious globalised economy. But Finland, Estonia, even tiny Trinidad and Tobago, with a population of only 1.3 million show that it is possible to be independent, innovative and economically successful. Scotland, as the eminent scholar Sir Tom Devine has pointed out, has undergone "a silent transformation of the economy". It now includes renewable energy, light manufacturing, electronics, tourism, financial services and the creative industries plus a thriving sector in higher education.

In a speech on Friday, Lib Dem peer Baroness Shirley Williams set out a strong case for maintaining the union: "The shared heritage of the rule of law … the commitment to the liberty of the individual, the constraints of a constitutional monarchy, these are not values to be taken for granted. For most of the world we live in, these are at best aspirations. For us, voluntary members of a lasting union, they are the foundation of a stability and security that is beyond price."

Those voting in favour of Scottish independence on Thursday will need to be certain that separation is a better option than a federated Britain, granting citizens in every region the strongest voice yet and an opportunity to challenge the political establishment. It would be inspiring to think that the radical energy generated by this referendum could see the whole of the UK becoming a fairer and more enlightened place. The extraordinary drama of this referendum means that there will be no return to the status quo ante south of the border. Given Scotland's historic attachment to values of social solidarity and its capacity to produce leaders and thinkers of talent and distinction, it would be all the more compelling to think that Scotland would be part of this renewal. That Londoners, Mancunians and Glaswegians will work together to re-make Britain in such a way that all its regions are empowered, and all its people written firmly and fairly into a new union.

A new political settlement for the union offers a convincing opportunity of a new start for the whole of Britain. On Thursday, Scotland will decide but, whatever that choice, Britain will not be, and should not be, the same again.