The parties are planning their campaigns for next May – but without knowing what the voters really think

Driving through Trafalgar Square just before the 1979 general election, James Callaghan, the Labour prime minister, reflected to his aide Bernard Donoughue: "Sometimes it does not matter what you say or do, there is a shift in what the public wants and what it approves. I suspect there is now such a sea change, and it is for Mrs Thatcher."

One year before the general election in May 2015, few outside the core of blind party loyalists would pretend British politics has reached such a settled state. There is no tide in the affairs of men, just eddies springing, swirling and dissipating. Britain may have an army of pollsters and, for the first time in its history, a fixed date for the general election, but the outcome is perhaps the least predictable of any in postwar history.

Political strategists are drafting and refining their campaign war books for the coming 12 months. Battle plans, ad agencies, grids and dividing lines are being prepared for the long and short campaigns and, for once, the strategists, even the coalition-seeking Liberal Democrats, can believe with reason this is not an act of futile vanity.

What happens between now and polling day matters. Events, dear boy (and girl), are there for the parties to shape and win. Yet on all sides there is a wariness about reading the public mood. The public's evident disconnect with politicians is felt as much in the other direction. The politicians are grappling to gauge the public mood – the depth, permanence and source of the popular revolt reflected in the rise of Ukip is only a symptom of a wider malaise.

James Callaghan, the prime minister before the 1979 general election, accurately predicted that the British people wanted Thatcher in power. Photograph: Rex Features

In the short term, The Great Unknown is whether the European and local elections will turn out to be a frolic, and the serious business of politics, as senior Tory Ken Clarke put it last week, will thereafter return. On the morning after polling day, will a sheepish nation wake up, hurriedly smooth its dishevelled clothes, apologise for the one-night stand and agree not mention it, or Ukip, again?

That has been the case in the past. The thinktank British Future points out that Ukip won more than 16% in both 2004 and 2009 European elections, but fell to 2-3% within a year. Even as the number of people voting almost doubled from the European to the subsequent general elections, Ukip shed almost 2m votes.

Now, though, Ukip's appeal has a new durability. Prof John Curtice from Strathclyde University pointed out: "Ukip has demonstrated an ability to retain most of the support that it garnered in the months leading up to last year's local elections. After briefly reaching a high of 15% in the immediate wake of those elections, the party has consistently registered around 11% of the vote since July last year and, in the last month, has seen its support rise once again to 13%."

In many European polls, Ukip standing is closer to 28%, at least among those who say they are totally certain to vote. The early tremors of the political earthquake so often promised by its leader Nigel Farage can already be felt.

David Cameron already has his response prepared for after the European elections. First off, he is going to close parliament, albeit for two weeks. From 21 May, on the eve of polling day, to 3 June, his MPs are being sent to their constituencies to minimise the backbench plotting, calls for a pact with Ukip and general collective hysteria.

On the Saturday after the polls, armed with the local election results and exit polls on Europe, George Osborne will deliver a keynote speech to the ConservativeHome conference. The chancellor will make an assiduous attempt to say "lessons learned, lot more to do in the parliament's final year and time for the Eurosceptic family to come back together".

A cabinet reshuffle will be prepared. Boris Johnson may even choose this dangerous moment to declare his indecision is no longer final, and will answer the Call of Duty, and stand for parliament.

Cameron intends to close parliament from 21 May, on the eve of polling day, to 3 June, and send MPs to their constituencies. Photograph: Zuma/Rex

But this firewall strategy has flaws. The unexpected Newark byelection is now on 5 June, inviting another weekend of introspection if the Ukip bubble has indeed kept growing.

These byelections and local elections have become a gateway drug for Ukip voters who may now stay with the party next year. More than half – 55% – of Ukip supporters say they are very likely to vote for the party in 2015, according to a ComRes poll last week. Cameron's Operation Detach is not going to be easy. Cameron's strategic Ukip dilemma – tack with the wind or confront – will remain.

Cameron's allure will not be helped if Andy Coulson, the man he controversially chose as Conservative director of communications, is found guilty by a jury of phone hacking. The verdict in the long-running trial is expected in June.

But the long summer will not just be a testing moment for Cameron. Nick Clegg's "party of in" faces the prospect of being the party of out at the European elections, losing all 12 of its MEPs. Curtice predicts it will retain precisely two MEPs. Senior Liberal Democrats reckon they may hold three seats, one each in London, South West and South East England. "Wipeout is feasible. The margins are very fine," said one activist.

The local elections could be just as bloody. Colin Rallings and Michael Thrasher, the gurus of local elections, have predicted the Liberal Democrats will lose 340 of their 732 seats being contested in this round. Inside the party, that figure is seen as only a little high.

As a result the jury is now out on whether Clegg's decision to challenge Farage to a TV debate was right. At the time it seemed politically brave. It motivated the party's activists. But it may also serve to remind his party how much his personal appeal has shrivelled.

Lord Oakeshott, Clegg's most outspoken Lib Dem critic, has said the party must leave the coalition after the elections, claiming it is "in great danger" and its distinctive message drowned. But the Lib Dems have most invested in showing coalitions can work and that the experiment is worth repeating after 2015. The party will probably stay the course. Clegg himself will try distraction, urging the party to focus on policies for the manifesto. "It's called the 'look over there, something is shining' strategy", one critic said.

It is hard to overstress the links the Miliband team, pollsters, intellectuals and strategists see between US and UK politics. Photograph: Graeme Robertson

Either way the business of the coalition will become harder to transact as relations become more fractious. The rules of collective responsibility will fray as one wing of the coalition disowns responsibility for the work of the other. For civil servants caught in the crossfire, there will need to be clearer rules on impartiality, as an Institute of Government report due out on Wednesday suggests. Some civil servants are already disengaging, saying neutrality is becoming an impossible aspiration.

The one binding force keeping the coalition together by mid June will be the looming vote on Scottish independence on 18 September. The formal referendum period starts on 30 May, just as Scots digest what may prove to have been the most potent display of English nationalism since that of Enoch Powell in 1968.

The polls in Scotland already show some narrowing, and unionists' nerves are fraying because they fear it will get worse. In most referendums, undecided voters tend to drift into the conservative camp towards the end of the campaign, but Scotland's independence vote may be an exception. Undecided voters are more leftwing than the typical Scot, more hostile to the Conservative-led governments down south and more willing to imagine Scotland succeeding alone. In short, they are "almost undoubtedly more favourable to independence", according to Curtice.

Many MPs are convinced the union is in true peril, with some expressing dismay that the Conservative party has become such a dissuasive voice for the union in Scotland. "The Better Together campaign is just ramshackle. It would not matter if it was just crap, but it is nasty. All the threatening from Whitehall has been counterproductive," one said.

Inside the Labour wing of the no campaign, if the polls narrow, the disagreements will sharpen between those who want to focus on what is best for Britain and those such as Gordon Brown who say the campaign must concentrate on the options for Scotland.

A vote for secession would probably lead to a parliamentary inquest as long as the seven-year trial of Warren Hastings in the wake of the collapse of the East India Company. In the short term, as custodians of the English elite, Ed Miliband and Cameron would take the bullets. Cameron would be vilified as the prime minister who allowed the union to be lost. Miliband would be attacked for breaking Labour's connection to the Scottish working class.

The party conference season, starting with Labour immediately after the referendum itself, would have the feel of a three-week wake for a 300-year-old union.

Nick Clegg's 'party of in' faces the prospect of being the party of out at the European elections. Photograph: Danny Lawson/PA

If the joint message of the May elections and the September referendum were one of separation – Britain out of Europe, and Scotland out of Britain – the identity of the English political class would need rethinking. Disoriented politicians would have less than six months to work out what to tell the electorate in 2015, before the two countries cast themselves adrift in 2016. Labour would lose 40 seats – and an intellectual tradition.

But the presumption remains that it will be Alex Salmond who tastes defeat. The Labour machine will get its voters in the central belt to look over the abyss of secession and recoil. That would clear the way for the long run-in to the general election, opening the argument about the economy, starting with the autumn statement. Logic suggests Cameron must win an election in which Labour is still held responsible for the crash and the Conservatives month after month point to economic figures showing the wisdom of Osborne sticking to the austerity course in the first four years. Even now the Labour poll lead seems to be defying gravity, and it seems inconceivable that will still be the case by late autumn.

Yet Labour says that is to misunderstand both how voters think and what is happening in the economy. One of Miliband's pollsters, James Morris, recently wrote: "Some think the 2% growth predicted by the OBR [Office for Budget Responsibility] for 2015 is David Cameron's ticket back to Downing Street. Growth is not enough for victory. The last US electoral cycle saw [presidential contender] Mitt Romney ahead on 'the economy' (though it did narrow right at the end). It was Obama's lead on being for ordinary people that carried him through."

It is hard to overstress the links the Miliband team, pollsters, intellectuals and strategists see between US and UK politics. In America in 2012 Obama did not win by seeking credit for a recovery, but instead by saying the recovery was not working for most people and that only he, not Romney, could fix this. In December 2011 Obama travelled to Osawatomie to give a major speech in the same small town where Teddy Roosevelt gave his 1910 New Nationalism speech.

The depth, permanence and source of the popular revolt reflected in the rise of Ukip is only a symptom of a wider malaise. Photograph: Jeff Overs/BBC/PA

In words familiar to anyone who has followed Miliband's thinking, he said: "Long before the recession hit, hard work stopped paying off for too many people. Fewer and fewer of the folks who contributed to the success of our economy actually benefited from that success. Those at the very top grew wealthier from their income and their investments – wealthier than ever before. This is the defining issue of our time – this kind of gaping inequality gives lie to the promise that's at heart of America that this is a place where you can make it if you try."

In particular it was Obama's portrayal of the Republicans as the champions of the 1% and failed trickle-down economics that won through. On-your-side politics sometimes trumps everything.

Miliband is taking the gamble that voters will put aside doubts about his personal credibility and be receptive to a British version of this message. So the election becomes not just a matter of competence, and the maths of the deficit, but about reconstructing a fair economy. This has to be a recovery for the whole nation, and that means a different kind of regulated capitalism.

For the Conservatives, the balancing act is difficult. The country is not ready for a Reagan-like "Morning in America". Optimistic assertions that "Britain is back" still do not chime, certainly outside the south-east, and are certainly unwelcome from the party of the rich.

But at some point over the next 12 months the recovery will be felt. Wages are going to creep ahead of prices, unemployment will continue to fall, interest rates will remain low and economic optimism will rise. Even if the recovery is fragile, Osborne will offer security against the risk of Labour.

He can then with greater confidence unleash his argument most confidently expressed in America last month that markets work and that by lowering corporate taxes and cutting spending, the British government has shows businesses it is safe to invest in the UK's economy.

He will have the backing of the press and donors, as well as one of the most aggressive campaigners in modern politics.

In the end it may depend on the state of Conservative party morale by election day, and whether it has held together through the storms of the previous year. In his diaries, Donoughue recalls how the Callaghan government fell apart in 1979. He concluded: "It strikes me how governments are beaten from within and not without. The Tories have never done us this kind of damage and nor did the IMF. The present demonisation arises from within the Labour movement and the cabinet itself."

• 2015 post-election scenarios