It was just like old times. Jeremy Paxman was back where he belongs, on the television toying with politicians for sport, making the prime minister and leader of the opposition look like cubs who’d recklessly wandered into the den of an aged lion — one who had not lost his appetite for raw meat.

The broadcast was so nostalgic it was almost comforting. The not-quite-a-debate was a throwback to politics the way it used to be: two men, two parties, neatly colour-coded for simplicity, the red and the blue teams facing off in a binary choice.

If anything, there was frustration that the encounter was not binary enough. The pundit class was agreed: there should have been a head-to-head, US-style presidential debate, pitting the two leaders against each other in direct combat. Miliband’s “Am I tough enough? Hell, yes ” seemed scripted for just such an occasion.

Next Thursday the frustration will deepen. ITV will screen an event that the Westminster village has written off in advance. That’s because it’s not a debate in the Nixon v Kennedy mould, but a seven-headed hydra that will be more Borgen than West Wing. The political chatterati already agree: it’ll be a disjointed, incoherent cacophony, simultaneously turning off the voters and belittling the politicians, reducing them to seven dwarves behind lecterns. Forget Obama v Romney. This will be pointless.

It may be bad TV, and yet of the two this is surely the more fitting format. It’ll be a mess. It’ll address half a dozen subjects at once. The combatants will be speaking at cross-purposes. Which is why it’ll be a perfect reflection of the state of British politics in 2015. For ours is no longer the two-party system that in 1951 saw 97 per cent of votes go to either Labour or the Conservatives. That vanished long ago. It’s not even a three-party system, not when polls show the traditional third party, the Liberal Democrats, slumping in their share of the vote (even if they do cling on to a decent number of Commons seats). We are now in the era of four-, five- and six-party politics. Throw in Northern Ireland and you’re into double figures. We have begun to speak of not one election but at least five, each with its own shape and dynamic

More than just numbers

But it’s about more than just numbers. In the Guardian’s preparations for the campaign that formally begins on Monday, we have begun to speak of not one election but at least five, each with its own shape and dynamic, distinct from the others. Most obvious is the battle for Scotland, where polls suggest a fundamental realignment. The prime contest there is between Labour and the Scottish National party, the latter apparently on course to wipe out the former — replacing it as the dominant Scottish force not only in the Edinburgh parliament but at the UK level too.

Where once Scotland divided between Labour and Tory, after last September’s referendum the key fault line runs between unionist and nationalist — with Labour apparently on the wrong side of the divide. If Miliband clashes with Alex Salmond on Thursday, it’ll be this fight that will be played out.

Meanwhile, England hosts several different elections at once. In much of the east, especially in the coastal towns of East Anglia, combat will come down to a two-handed struggle between Ukip and the Conservatives. In parts of the north-west Ukip will be taking on Labour. In the south-west, the Lib Dems join the fray, often facing down their erstwhile Tory partners in coalition. London has its own contours: less Ukip, perhaps more Green. And in Wales, Plaid Cymru will dream of playing the SNP’s game, casting Labour as the party of a reviled Westminster establishment.

The sheer complexity of all this will be painfully visible on Thursday. David Cameron might want to craft a message of inclusivity to appeal to the London marginals — but how to do that with Nigel Farage over his shoulder, itching to woo those one-time Tories disaffected at the changing face of Britain?

Miliband might want to pander to voters in England, but he’ll get a death stare from Salmond if he tries. If the Labour leader tacks right to head off Ukip on immigration, Natalie Bennett of the Greens will be ready to pounce. If he tacks left to appeal to the Green-curious, Farage and Cameron will seize the opening.

Voters are wise to this new landscape. If anything, they’ve grasped it more quickly than the political professionals. New research from Manchester University’s British Election Study released today found that voters who expect a hung parliament — and 41 per cent do — are much less likely to vote Labour or Tory. You can see why. A vote for one of the big parties seems a waste if they are only going to go into coalition and dilute their programme. Better to vote for a smaller party, one that fits your ideological shape more closely — not least because that vote will have, as the study’s authors put it, “more clout” if those parties become kingmakers in a hung parliament.

The new fragmentation will be on vivid display on Thursday, embodied by a TV screen crammed with candidates jostling like market traders forced to share a single pitch. But their competing sales patter will reveal more than the unfamiliar, crowded chaos of contemporary British politics. It will also point up two themes that are increasingly likely to dominate our national conversation.

First is nationalism. The SNP already dominates Scottish politics, but now it’s set to displace the Lib Dems as the third force in Westminster. Separatism can no longer be haughtily dismissed as a question for the fringes: it will sit at the heart of UK politics. And it’s not just the SNP (with Plaid in its wake). For what is Ukip if not a nationalist party? It claims to speak for more than English nationalism, but that’s a subtlety often lost on its supporters.

The second theme is related. When Cameron and Farage clash on TV, it will be to outdo the other in Eurosceptic fervour — the prime minister stressing that, for all the Ukip leader’s posing, only he can deliver an in/out referendum in 2017. This, surely, is one of the key choices of May 7. If Cameron returns to Downing Street, the country will be plunged into a two-year debate about its identity, its place in the world, its future and, inevitably, its past. If Miliband gets there, it won’t. Some of this epochal choice is bound to bubble through when Cameron, Farage and Miliband share the stage.

Of course, a duel is more fun to watch than a 14-legged scrum. But that’s no reason to recoil from the noise, mess and complexity we’ll see next week. On the contrary, it will be a good guide to who we now are.

— Guardian News & Media Ltd