During the final yomp through the election battlegrounds, David Cameron will be adapting the motto of the SAS. Who Scares Wins. The Tories will try to put the frighteners on the floaters. Fear is now their best hope of squeaking a parliamentary majority on a minority of the vote. They want to chill the blood of voters with the allegedly calamitous consequences for Britain if the election does not produce a clear winner.

The logic of David Cameron's argument against a hung parliament is that if the voters won't supply a "strong and decisive" government by giving him a Commons majority, then they ought to hand one to Gordon Brown or Nick Clegg. The Tory leader does not, of course, want us to think that. When he says Britain will be let down if there is not a single-party government, he means it will be unpatriotic not to vote for him, a contention at once presumptuous and condescending. This at least clarifies the invitation "to join the government" which he first issued at his manifesto launch. Anyone can join so long as they vote Conservative.

One Tory tactic will be a traditional technique of the late campaign: the third party squeeze. To voters who have boarded the Cleggwagon, the Tories warn that they could end up inadvertently putting Gordon Brown back in Downing Street. Vote Yellow. Get Brown. The Tories will turn up the volume of that claim in the climactic days. I am sceptical that this will work as effectively as it has in the past. The proposition that Gordon Brown could limp back to Number 10 seems very implausible unless there is a dramatic shift between now and Thursday. At the final leaders' debate, he conceded that "if things stay as they are", he will no longer be prime minister, breaking the cardinal rule of electioneering that you should always maintain that you are going to win. In the wake of his self-inflicted humiliation on a Rochdale housing estate, this prime minister looks like a boxer who has been hit once too often.

I am among those who have made jokes about him only relinquishing his grip on the doorknob of Number 10 when all his fingers are broken. The perversities of first past the post do throw up permutations in which Labour comes third in the vote and yet ends up with the most seats in the Commons. But no one serious in any party thinks Mr Brown could cling on for anything more than a brief transition period in those circumstances. The sharpened presidentialism of the contest because of the TV debates makes this election even more of a personal verdict on the leaders. Nick Clegg was tactically smart to say that he would not let a third-placed Gordon Brown "squat" in Downing Street.

For Labour, too, fear looks like their last hope. Peter Mandelson argued, in a campaign memo released yesterday, that the election will be decided in a 100 Labour/Tory marginals. "To those flirting with the Lib Dems in these seats, we need to make sure they know that a Lib Dem vote is the surest route to a Tory government." Vote Clegg. Get Cameron. Labour will turn up the amplification on that claim. There is certainly a dilemma for Lib Dem supporters in seats where Labour still appears to be the principal opponent to the Conservatives. Do they vote Lib Dem nevertheless in order to maximise their national vote, strengthen its case for electoral reform and boost Nick Clegg's bargaining power in a hung parliament? Or do they lend a vote to Labour to make it harder for the Tories, the party most implacably opposed to reform? Labour has been loaned a lot of these votes at the last three elections. If they want to borrow them again, the Dark Prince will have to find a more persuasive appeal to Lib Dem voters.

The classical squeeze on the third party will be much harder to execute in a volatile election that has turned out to be anything but traditional. As most of the opinion polls stand now, the Lib Dems are no longer the third party anyway. That unenviable distinction belongs to Labour. There is barely concealed terror at senior levels of the party that they could come third in a general election for the first time in exactly a century. Nor do the Conservatives have an utterly unambiguous claim to be the first party when some polls have the Lib Dems breathing down their necks. Nick Clegg is even making the bold assertion that Labour is effectively out of it and the contest has turned into "a two-horse race" between himself and David Cameron. The Lib Dem leader may be getting a bit ahead of himself, but I can see why he is relishing being able to say this. After decades when they have been the victims of the squeeze, the Lib Dems are at last in a position to flip that game back on Labour and the Tories. At countless byelections, the Lib Dems have prospered by turning themselves into the vehicle to defeat one of the other two. "A Labour vote is a wasted vote," they will say in Tory-held constituencies. "Tories can't win here," they will say in Labour-held constituencies. In the remaining days of the campaign, Nick Clegg's dream is to turn the general election into one enormous byelection.

Since Gordon Brown is of fading use to the Conservatives as a bogeyman, the Tories will endeavour to scare the swingers with another spectre. Be very afraid, they will tell us, of a legislature in which no one party wields absolute power. It will be the worst fate to a befall Britain since the Black Death – or, at any rate, since the 1970s. David Cameron avers that supporting the Lib Dems will be "a vote for uncertainty". In truth, a cross in the box for any of them will be a vote for uncertainty. None of them has said how they will bridge the huge gaps in their plans to tackle the deficit which were recently identified by the Institute of Fiscal Studies. All three have been economical with the truth about the tax rises and spending cuts which will follow whatever the result this Thursday.

Alistair Darling has been candid enough to warn that the spending squeeze will be more severe than that implemented by Margaret Thatcher in the 1980s. She came to power with 44% of the vote. Even if the Tories do manage to achieve a parliamentary majority, I can't find many Conservatives who expect to match the Thatcher vote share in 1979. Since neither they nor anyone else has any chance of winning half of the popular vote – or even remotely close to it – no party will have an unarguable mandate on 7 May.

The governor of the Bank of England is reportedly of the view that this is an election to lose because whoever finds themselves in office will become so unpopular that they will thereafter be out of power for a generation. Many voters have already intuited that resolving the economic challenge and reforming politics are burdens of responsibility too heavy for one party ruling in splendid and very unpopular isolation. The polls indicate that a substantial number of voters, even half of the country, actively desire a result which denies absolute power to any single party.

The derogatory term "hung parliament" is rather peculiar to Britain. In most mature democracies, it is taken for granted that one party will rarely be so popular that it gets to rule on its own. Germany has been governed by coalition governments for most of the time since 1945. Germany has been no less stable – and in some respects rather more – than Britain. Its economic performance has also been superior. The Scottish parliament has been "hung" from its establishment in 1999 to now. It produced a durable Lab-Lib coalition for the first eight years and then the current three-year-old Nationalist minority administration. The sky has not fallen in.

You might argue that these examples don't exactly read across – and I agree they don't entirely – to a Westminster government faced with tackling an enormous deficit. It is indeed a massive challenge, but not the greatest that has ever faced this nation. Britain's time of gravest peril in the past 300 years was the Second World War. Winston Churchill successfully thwarted the threat of Nazi invasion and led his country to victory – at the head of a coalition government. Co-operation was strength at a time of national emergency.

A single party trying to rule on its own after an election in which support was so evenly spread between three parties will be at risk of being crippled by a lack of legitimacy even before it begins to make some excruciatingly painful choices. Which would actually be stronger and more durable? A government with a fragile parliamentary majority or no majority at all which came to power with the support of a minority of voters? Or a coalition or other arrangement between two parties which could rightly claim that they represent, between them, a much wider range of voters and many more of them?

The Tories currently decry coalition and so do many Labour voices. By the morning of 7 May, it might suddenly look rather attractive to share responsibility for inflicting the cuts with a partner. Perhaps the better question to ask during these final days of campaigning is whether the Lib Dems actually want to take up that burden.

• More election comment from Cif at the polls