At surface level it has looked like every other election. Indeed, at times, it has been the distilled essence of them: the high camp of the TV bulletins camper, the staged public appearances of the leaders stagier. Yet the 2015 general election is about to unleash profound change.

The polls have not moved, so we’re about to get the second hung parliament in succession, in a system that never used to produce them. Only this time we don’t just get a coalition government. We get an existential crisis of the constitution, and of the UK as a political entity, that no political party is currently geared up to deal with.

To understand why, you have to recognise the demographic tribalism that an economic system in crisis has produced. I’ve written about this before: the division of England into an asset-rich south, a post-industrial north and the emergence of a positive national consciousness in Scotland linked to the rejection of neo-liberal economics.

The old party system began to dissolve almost as soon as the neo-liberal model took off. A free-market economy, oriented to Europe, was always going to split the political right, with an anti-global, socially conservative and plebeian wing uncontainable within the Conservative party. Indeed, it was the Tories’ inability to decide what they stood for on Europe and social liberalism that destroyed John Major’s government and kept the party out of office for a generation.

Blair and Brown governed for so long because they were able to reach across the divide that the economy was creating. And this was not just an act of reaching, but of papering-over with deficit spending. Once the crisis hit, and there was “no money” left as Liam Byrne so candidly explained, New Labour’s balancing act would have been hard even if the three political tribes of Britain were not spinning apart from each other. But they were.

Let’s do a thought experiment: what kind of leader, and policies, would it take for one or other of Labour or the Conservatives to create, again, the kind of hegemonic political alliance Blair created?

For the Tories, it would need somebody capable of inspiring, and delivering to, the post-industrial communities of England and Wales; giving enough working-class people a material stake in the wealth created so that the political balance in the working men’s clubs and factory floors tipped rightwards.

For Labour, the route to majority government now can only lie through Scotland and the affluent towns of southern and middle England. While some Labour strategists agonise over its loss of working-class heartlands such as Harlow, that’s not the main problem. The main problem is that Labour – having reshaped social democracy around a policy of fiscal largesse – cannot work out what to do when fiscal largesse is ruled out. To complete the thought experiment, you now have to imagine what would happen inside the two main parties, and to the economy, to produce this new, divide-crossing single-party government.

It’s not going to happen. Instead British politics is entering a phase where the reality of coalition government, and the increased likelihood of Scottish independence, has to reshape the politics, personnel and structure of the main Westminster parties. They will need to stop talking as if coalitions and Scottish separatism are accidents, or illegitimate, and re-attune to their permanence.

It may take a while to sink in after Friday, and may take another election, but at some point in the future British prime ministers are going to have to be different kinds of people: ones who can lead coalitions rather than ones who can win and maintain control over a party machine.

In future, party leaders will have to honestly accept coalition government as a likelihood from day one of an election campaign and thus that their own manifesto will become a series of suggestions, with a limited number of “red line” issues to guide the electorate as to their principles in coalition negotiations.

But that’s only the least mind-bending of the changes ahead. For the past five years politics has become reduced to fiscal policy: debt, deficit, taxation and public spending. In that sense it has been unusual, and will soon change. On all parties’ spending plans, the deficit disappears by 2020, and as it does so politics will have to start addressing the big issues that the 2010-15 parliament effectively sidelined: Britain’s security in a fragmenting global order; its economic identity; its model of social justice; and, above all, how democracy and the rule of law function in an era of unaccountable global elites and negotiated coalition rule.

Given the momentum of Scottish separatism, and the scale of fiscal autonomy that will be needed to assuage demands for independence, Britain is probably set to become a monetary union. There will be separate tax and spend regimes in Scotland and Wales for certain, and probably in the English regions, backed by a single monetary authority and shared currency. So monetary policy is going to be re-politicised.

Once Britain is a monetary union, not a fiscally unified state, then it is also, effectively, a “defence union”. The renewal and future siting of Trident, and the deployment of armed forces in expeditionary wars, become de facto negotiated decisions and not the absolute right of a prime minister in Downing Street, or of a simple parliamentary majority.

Indeed, rule from Downing Street will have to take place alongside new or changed institutions that can govern Britain as a fragmented political space.

On Friday, unless there is some survival-level political event before then, the two biggest parties will have to wake up to this new world. Neither will want to, but the one that wakes up first will get a head start in the game that begins on 8 May. The game is, quite simply, adapt or die.

Paul Mason is economics editor of Channel 4 News. Follow him @paulmasonnews Read his blog here.