In the dim and distant past of about three weeks ago, this election was supposedly called in order to settle Brexit. Britons have been repeatedly told that they are going to the polls for the third time in less than four years to resolve the great issue once and for all.

“Get Brexit done” has been the incessant mantra of Boris Johnson from day one of the campaign. He repeated his already hackneyed catchphrase so often during the first of the TV debates with Jeremy Corbyn that the audience was audibly groaning by the end. “Get Brexit done” will be the thumping beat of the Tory manifesto. Yet there is no more deceptive slogan of this campaign. This “Brexit election” is leaving Britons none the wiser about where their country will eventually land.

It will be “done” only in a very limited sense if Mr Johnson is returned to Number 10 with the Conservative majority that he craves. Though there will be some residual Remainers on the Tory benches in the next parliament, they will not feel able to stand in the way of a prime minister re-elected with a majority. Nor should much be expected in these circumstances of opposition parties that will be preoccupied with recriminatory postmortems about why they lost. It is a fair bet, then, that a Johnson majority government will get the withdrawal agreement that he negotiated with the EU through the Commons, probably in time to have the UK out by the end of January.

It cannot be said often enough that this will not be the end of the Brexit saga. It will not even be the beginning of the end. It will be merely the end of the beginning. The withdrawal agreement covers only the terms of the divorce and a period of transition thereafter. It says little definitive about the future relationship between Britain and its closest neighbours and most important trading partners. Those voters who are planning to pick the Tories in the belief that they will never have to hear about Brexit again are in for a disillusioning experience.

The Tory leader’s blather about securing “a fantastic new trade agreement with the EU” leaves it entirely unclear exactly what kind of future relationship he would be able to negotiate. Some Tories, including Mr Johnson himself on some days of the week, speak as if they want to maintain a reasonably close relationship that would see considerable continuing alignment with the EU on regulations and standards, consumer and environmental protections. Britain will have to agree to that if Mr Johnson really wants a tariff-free deal. That would still be a pretty hard form of Brexit that would impose considerable bureaucracy and costs on British businesses, but it won’t be hard enough for the hardliners, some of whom now occupy senior seats in cabinet. The ultras want a bare bones free-trade deal with the EU, a “Canada-minus”. If Mr Johnson is returned with a slender majority, the ultras may take him hostage, just as they did poor old Theresa May. The ultras will demand that Britain diverges from the EU as much as possible in pursuit of their vision of turning the UK into a Singapore in the North Sea. That would increase the chances of the negotiations collapsing. What worries European leaders most is having the single market and their economies undermined by a thin-regulation, low-tax, cut-price-labour Britain sitting off their north-west shore.

This next and tough round of bargaining comes with a deadline attached, which is 31 December 2020. A year is a short time in international negotiations of this magnitude and complexity. All of the recent free-trade agreements that the EU has struck with significant economies have taken at least three years to conclude and several have taken much, much longer.

Before talks can start, all 27 of the EU leaders will have to sign up to a negotiating mandate. Each will have interests to advance and domestic audiences to satisfy. Many have incentives to play hardball with the UK. These talks will not be conducted under article 50, but under article 218, which means that any deal will have to be ratified by every EU national parliament and by several regional ones.

The transition can be extended to the end of 2022, but a request would have to be made by next July and Mr Johnson has anyway flatly ruled it out, a declaration he made when seeking to persuade the Brexit party to fold its tents. So, very early in the life of a re-elected Conservative government, we would be back to ticking clocks, brinkmanship, showdowns and cliff edges, probably accompanied by a lot of angry cabinet rows about what kind of compromises and trade-offs are acceptable to achieve an agreement. And if there were no resolution by the end of 2020, Britain would once again be facing the calamitous prospect of crashing out of the EU with no deal.

Mr Corbyn doesn’t like talking about Brexit because it means ridicule for refusing to say whether he's for or against it

The Lib Dems cannot be accused of obfuscation. They have declared that a Lib Dem majority government would simply revoke withdrawal and keep Britain in the EU without any further reference to the people. This is clear. It is also fantastical. Even Jo Swinson doesn’t think Jo Swinson will be going to Buck House to kiss hands with the monarch on 13 December. Having seen their poll rating squeezed down over the past month, the Lib Dems are pivoting back to being a party campaigning for a second referendum from an unambiguously Remain stance, the policy they should always have stuck with.

Labour could be poking holes in the Tories, but won’t because Jeremy Corbyn wants to spend as little time as possible talking about the issue that divides both the party’s voters and its frontbench. He also doesn’t like talking about Brexit because it means ridicule for his adamantine refusal to say whether he is for or against it.

Labour has adopted the slogan “get Brexit sorted”, an imitative echo of the Tory mantra. Mr Corbyn claims he could secure a further extension to the withdrawal deadline, open and conclude fresh negotiations with the EU and then put whatever new deal he comes up with to the people in a referendum – all within six months. The sort of deal Labour talks about involves a customs union and close alignment with the single market, so it would be softer than any Tory version of Brexit, but it would still be Brexit. The Labour position raises a host of unanswered questions. If Labour aimed for a Norway-style deal with the EU, that would entail accepting the continuation of freedom of movement, about which the party high command is split and its manifesto ambiguous. And why would the EU engage seriously with a Labour government if the leader of that government declines to commit to recommending any new deal to his own party, parliament or country?

Even the more optimistic of Labour’s campaigners reckon being the largest party in another hung parliament is at the maximalist end of what they can achieve. To function, a Labour minority government would be reliant on the grudging acquiescence of the Scottish National party or the Lib Dems or possibly both. The Lib Dems would obviously support a fresh referendum. So would the SNP, but they would try to use any leverage in a hung parliament to extract a commitment to another referendum on Scottish independence as well.

Labour would put its so-called “credible Leave option” up against Remain in its proposed referendum. Mr Corbyn’s latest line, delivered during the leaders’ Question Time on Friday night, is that he would adopt a “neutral stance”. I thought he was running for prime minister, not Queen. He presents himself as a conviction politician and yet is incapable of saying, or unwilling to reveal, where he stands on such a defining question. This is clearly a vulnerability, an exposed bruise that both the Tories and Lib Dems keep thumping because they know it makes the Labour leader look weak and furtive.

In the interview with John McDonnell that we publish today, the shadow chancellor gamely contends that voters might warm to Mr Corbyn because he is not trying to force “his own view down people’s throats” while accepting that Labour hasn’t done enough “to make sure the message gets across more clearly”. Trouble is, a party cannot have a clear message when its candidate for the premiership is impenetrable to light.

We keep hearing that this election is the most important in living memory. Yet on Brexit, the most important issue of this most important election, both Boris Johnson and Jeremy Corbyn are asking voters to go to the polls wearing blindfolds.

• Andrew Rawnsley is Chief Political Commentator of the Observer