One of my colleagues recently recalled that, in advance of the 2015 general election, we spent quite a lot of time preparing a run of spreads about what to expect from the Ed Miliband premiership. That Labour government happened only in his dreams and our abandoned page plans. This reminds us that the results of all of our recent elections have surprised expectations. This is not just because pollsters find it harder to get an accurate read on the electorate, pundits are often poor at deciphering the runes and voters have become less anchored to traditional allegiances. It is also because Britain’s archaic electoral system means that fluctuations in the intentions of small numbers of people can have a wildly disproportionate impact on the outcome.

The shift of a few percentage points of vote share either way between now and Thursday can make the difference between Boris Johnson being returned to Number 10 with something looking like a Tory landslide or Jeremy Corbyn negotiating with the Scottish Nationalists to cobble together support for a minority Labour government.

If we take a step back from the campaign frenzy and try to contemplate this from a longer perspective, a Conservative victory will be the more remarkable result in the context of history. The Tories are making a very big ask. They are seeking a fourth consecutive term in power. This is a request that the British electorate has granted only once in the history of universal suffrage. The Conservatives have been in office for nearly a decade. That would be a patience-sapping age in reasonably good times. These have been hard times. Economic growth has been anaemic, real incomes have been largely stagnant and an austerity has been imposed on Britain that even some Tories now concede was overdone.

Mr Corbyn comes up on the doorstep more often than Brexit as the reason among traditional Labour voters to withhold their support

Since 2017, there have been a record number of ministerial resignations, a symptom of the uncivil war that has racked the Tories throughout the period. They have done little else than wrangle over Brexit while infecting the rest of the country with their party’s toxic divisions. Many of their moderates have been purged or fled. Sir John Major, the longest-serving living Tory prime minister, has effectively disowned his party. Michael Heseltine, deputy prime minister in Sir John’s government, is campaigning for the Lib Dems. In Boris Johnson, the Tories have a leader who can’t or won’t say precisely how many children he has fathered, a frontman with a fat back catalogue of incendiary and offensive remarks about key electoral groups and a candidate for the premiership who is laughed at by television audiences whenever the topic under discussion is trust. In normal circumstances, such a government under such a leader would be preparing itself for defeat and a well-earned stretch in opposition. Yet as we head into the climactic days of the campaign, it is the Tories who are the bookies’ and pollsters’ favourite to win. An obvious element of the explanation is Brexit, which has played better for the Conservatives than it has for their opponents. The most important structural development of the entire campaign came early when Nigel Farage, under great pressure from within his own faction, declared that the Brexit party was standing down in all seats which had a Conservative MP. This accelerated the migration of Brexit party supporters towards the Conservatives, uniting most of the Leave tribe behind Boris Johnson.

Of all the propagandising of this campaign, “get Brexit done” has cut through to the electorate more powerfully than anything else. This is an example of the potency of duplicitous tunes. As I’ve written before, it is the most mendacious slogan of the entire campaign. The Brexit agony endures if Mr Johnson secures a majority. It will be the voters who have been deceived into thinking that the nightmare will be over who will end up being done. The most difficult chapters of the negotiations about the UK’s future relationship with the EU lie ahead of us, with a no-deal outcome a very live possibility. But in order to win a British election you don’t have to be able to fool all of the people all of the time. You only have to fool enough of the people at election time.

Boris Johnson: ‘A candidate for the premiership who is laughed at by television audiences whenever the topic under discussion is trust.’ Photograph: BBC/PA

Doing the fooling is always so much easier if you are up against an opponent with even less credibility than yourself. In Jeremy Corbyn, Labour offers a candidate for Number 10 who has achieved the astonishing feat of being even less trusted with the premiership than the incumbent. If the Tories win this election, no account of their victory will be complete without analysing the critical role played in that outcome by their greatest collaborators, the Corbynite cadre who control the Labour party. After nearly a decade of often chaotic, frequently failing and bitterly divided Conservative government that has presided over an era of austerity, this ought to have been an election the principal party of opposition had confident hopes of winning. Yet Labour ends this campaign as it began: trailing the Tories. Its fantastical wishlists of promises are not believed and it has a candidate for Downing Street who plumbs depths of unpopularity never previously visited by any British opposition leader.

Labour has put on some vote share since the beginning of the campaign, mainly, it appears, by squeezing Remain support away from the Greens and the Lib Dems, but it has risen only slowly and from a low base. The positive reassessment of Mr Corbyn that his cheerleaders claimed would happen has yet to materialise. Unlike in 2017, his personal ratings have registered little improvement. Two and a half years on, he is no longer the novelty that he was to many voters last time around. They have got to know him a lot better and what they have got to know they have generally disliked. I have talked to Labour candidates, especially those trying to defend against the Tory assault in the “red wall” seats in the Midlands, the north of England and Wales. They report that Mr Corbyn comes up on the doorstep more often than Brexit as the reason among traditional Labour voters to withhold their support. This bleeds into attitudes towards Labour as a whole, as voters ask themselves what kind of party would persist with having a leader who has allowed the poisonous spread of antisemitism and tells silly fibs about watching the Queen’s Christmas Day broadcast “in the morning”.

Mr Corbyn and his friends have failed to turn Labour into a party capable of marshalling an election-winning coalition of support. Nor have they made it a party that non-partisan voters feel comfortable about seeing in office. An important consequence of this has been to weaken the potential effectiveness of anti-Tory tactical voting. At the election of 1997, tactical voting was sufficiently powerful to cost the Tories around 50 seats. Lib Dem supporters and swing voters were willing to lend a hand to Labour candidates because they didn’t have serious problems with the idea of Tony Blair as prime minister. Encouraging tactical voting is much tougher when moderate voters have several extremely large problems with the idea of Jeremy Corbyn and his cabal getting their hands on the levers of power. The data suggest that a majority of Tory Remainers will stick with the Conservatives at this election. You have to suspect that these anti-Brexit Tories, a significant proportion of the electorate, might have been a lot more biddable to the Labour party were it under a more attractive kind of leadership with a more credible suite of policies.

We should not rule out the possibility that there will be a swing to Labour in the closing days of the campaign, although it will have to be even more spectacular than in 2017 to deny a majority to the Conservatives. A late Labour surge may be more likely if the final polls suggest that the Tories are on their way to a substantial win. That might trigger a recoil against the spectre of a Johnson landslide that works to the benefit of Labour.

Yet there is nothing to celebrate about Labour having to rely on this sort of desperate calculation to give itself any grounds for optimism. Against a near-decade-old Tory government led by a man regarded as a charlatan even by many of those who are about to vote for him, Labour should be ending this election with high hopes of forming a majority government. It is instead frantically hoping that it might mitigate the scale of its defeat or squeak into office as a minority government thanks to the vagaries of our antique electoral system. And if the Tories win a majority they have done nothing to deserve, the lasting legacy of Labour’s Corbynite era will be another five years of Conservative government.

• Andrew Rawnsley is Chief Political Commentator of the Observer