There is only one reason why today’s election is happening: Brexit. Six weeks on, the 2019 election is still a Brexit election. You may want it to be about other things. You may be fed up and distressed with the whole Brexit argument. All this, though, is escapism. What is primarily at stake today is whether Britain leaves the EU on the Conservatives’ terms, or whether it doesn’t. Today, the nation’s votes will decide which it shall be.

The leitmotif of Boris Johnson’s campaign has been Brexit. For someone who loves to speechify as much as he does, Johnson’s message discipline has been awesome. “Get Brexit done” has been the “strong and stable” of the 2019 campaign. The slogan is brilliantly succinct and well chosen. But it is a fraud.

Johnson did not call the election because he lacked a parliamentary majority for Brexit. A Commons vote on 22 October showed that there was such a majority. But there was no majority for the unconditional departure from Europe that Johnson stands for, and which the rightwing of his party demands. This election is intended to create that majority and to weaponise the Conservatives as the leave party, on Johnson’s terms. All Tory MPs who are elected today will be bound to a manifesto that asserts “we will get Brexit done in January”, and “we will not extend the implementation period beyond December 2020”.

Yet those pledges are, respectively, untrue and unachievable. Getting Brexit done is the 2019 campaign big lie to set alongside the lie of the 2016 referendum about the NHS. It depends on the pretence that Brexit is a defined and deliverable object rather than a set of regulatory relationships that require negotiation, and which ought ideally to require final approval before they can be implemented. For its part, the December 2020 trade deal pledge is unachievable on the terms set out in the manifesto because the 12 months that lie ahead are not really an implementation period: they are a transition to a complex and unknown new relationship that has not yet been negotiated.

In other words, the central theme of the Conservative campaign – getting Brexit “done” – is a trick. We may think we know the likely result of the election – a Conservative victory. But we cannot know what the Brexit that Johnson promises, if he wins, would actually involve. This may be good enough for voters who simply want to pull the duvet over their heads, or for those who are so wealthy that the uncertainty would not affect them. But it is really terrible news for those who are directly affected by it, particularly in Northern Ireland.

Of all the fraudulent remarks Johnson has made in the campaign, none is potentially as lethal as the airy assurance he gave last week that there would be no checks or tariffs in either direction on goods travelling between Britain and Northern Ireland. This is yet another lie at the expense of Ireland, north and south.

About 75% of goods making that journey – many of them the lifeblood of small- and medium-sized businesses on both sides of the Irish Sea – will be liable to pay tariffs and checks on rules of origin. If the UK crashes out with no trade deal in a year’s time, those tariffs and checks will become more intense, not less. Even if there is a trade deal, it will take many more months or years to set up the systems to implement it, as the Brexit department leak last week shows.

It has been a familiar Conservative campaign line in the past month that because Johnson surprised the political naysayers by getting a revised withdrawal deal, he will surprise them again by getting a new trade deal. This is another total porky. Johnson got a revised withdrawal deal not because of his toughness, charm or brilliance but because he agreed to maintain the EU single market in Ireland, and create a border in the Irish Sea. He got a deal only because he folded on the EU’s terms.

Facebook Twitter Pinterest ‘All he can deliver are the worst consequences of Brexit.’ Boris Johnson speaks to the press on his campaign plane. Photograph: Stefan Rousseau/PA

In just the same way, Johnson will not be able to secure a new trading relationship with the EU in a matter of months without making a similar capitulation on the EU’s trade terms. The less he wants to diverge, the shorter the negotiations will be. But most of the Tory party wants Johnson to diverge as much as possible. That means a longer negotiation. The Johnson who wants to get Brexit done might actually be willing to concede to the EU. The party he leads is unlikely to give him that political space. So he will not get Brexit done after all, not without a breakdown with the EU. Unsurprisingly, this is Nigel Farage’s new cause.

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This has been an unnecessary election based on a false claim. It is a Brexit election. But Johnson cannot get Brexit done. All he can deliver is the worst consequences of Brexit – further destabilisation in Ireland, fresh separatist feeling in Scotland, a new iteration of division between leave and remain in England and Wales, more parliamentary conflict, renewed economic uncertainty for business and jobs, and the further humiliation of Britain on the world stage. The Conservatives created this mess, and they appear incapable of solving it.

The alternative is not simple either. But it exists – and it is better than anything Johnson will achieve. The alternative is to hold a confirmatory referendum on either the current deal or some other future deal. If the polls are right, most people today will vote for parties that offer this alternative. The only way to get Brexit sorted is to vote tactically for the party or candidate best placed to defeat the Conservatives. Forget all the rest. If the majority uses its power, Brexit can be stopped and Johnson can be thrown out. That’s a warming thought for a winter’s day.

• Martin Kettle is a Guardian columnist