When politicians can spread untruths with little accountability and few electoral consequences, an irreversible rot starts to set into the political system. There’s no greater indicator that this is happening in Britain today than the fact that a man within spitting distance of Downing Street is getting away with deploying utterly misleading information about what might happen in the aftermath of a no-deal Brexit, in order to strengthen his leadership bid.

In a leadership debate last Tuesday, Boris Johnson said that if Britain were to crash out of the EU without a deal, we could avoid paying any tariffs on imports from Europe. He claimed that there could be a “standstill” under article 24 of the World Trade Organization’s general agreement on tariffs and trades, which would allow the UK and the EU to get around the WTO rule that a country that eliminates tariffs for another country, outside of a comprehensive and mutually agreed free trade agreement, must also do so for all other WTO members.

Johnson’s claims contradict the views of trade experts. The House of Commons library summarises it thus: “Trade law experts have repeatedly and authoritatively dismissed the view that the relevant rule offers an easy solution to UK trade with the EU in the case of ‘no deal’.” So Mark Carney, the governor of the Bank of England, was entirely correct to reject Johnson’s assertion. If there is no withdrawal agreement when Brexit happens, Britain and the EU will have to trade under WTO tariffs, unless they choose to lift tariffs for other countries.

The only way to eliminate tariffs between the UK and the EU after a no-deal Brexit is either through a time-limited “interim agreement”, which other WTO countries have the power to block – it’s why no WTO member has used such an interim agreement since 1995 – or to negotiate a full free trade agreement that would likely take years to agree, not least because, unlike the withdrawal agreement, it would almost certainly require unanimity from EU states.

That Johnson is happy to wilfully mislead voters should come as no surprise. As the public face of Vote Leave in 2016, he claimed that leaving the EU would free up £350m a week for spending on the NHS, which saw the head of the UK’s statistics watchdog accuse him of “a clear misuse of official statistics”. During the campaign, he stoked fears that Turkey was on the verge of joining the EU, despite the fact its application had stalled, but earlier this year claimed that he said nothing about Turkey during the campaign. But his propensity to stray from the truth is doing little harm to his leadership campaign.

It is reflective of the extent to which no deal – certainly not the Brexit proposition presented to the electorate in 2016 – has become the Brexit of choice for hardline Tory Eurosceptics. Faced with the reality that the Brexit they presented to voters was only ever a fantasy, they have joined Nigel Farage in clamouring for a “clean” Brexit – in other words, crashing out of the EU. This has resonated with Conservative members: more than half say they prefer no deal to the withdrawal agreement. The two remaining Tory leadership candidates, Johnson and Jeremy Hunt, have been shamelessly playing to this crowd; even Hunt has said he would countenance no deal.

Of course, no such “clean” break from the EU exists. Britain is not legally prepared for a no-deal Brexit: at a minimum, the government needs to get at least five more bills through parliament. Britain would need to re-establish its independent status as a member of the WTO, not necessarily straightforward if other WTO members try to extract concessions. And the UK’s negotiating position with the EU would be significantly weakened: once we have left, a new transitional agreement would likely require unanimous agreement from EU states, including national and regional parliaments, rather than the qualified majority required for the withdrawal agreement under article 50.

A no-deal Brexit will have destructive economic and political consequences for the country. The government’s forecast is that it would depress GDP between 7.7% and 9.3% over a 15-year period and it is the least affluent areas of the nation that will be hit worst in terms of jobs and growth. Moreover, a no-deal Brexit risks the breakup of the UK; it would increase the pressure for a vote on Irish unity and fuel the campaign for Scottish independence. This does not seem to worry the Conservative members who will select our next prime minister. One poll last week suggests they are so ideological about Brexit that they are happy to countenance significant economic damage, the breakup of the union and the destruction of their own party in order to see it happen. Johnson is currently expected to secure a comfortable victory among them, despite the fact that 40% believe he cannot be trusted to tell the truth.

It has never been clearer that the Tories cannot be trusted on Brexit. In failing to rule out no deal, both Johnson and Hunt seem entirely unperturbed about its impact on the least affluent areas of the country. Why would they be, when they have been part of a government happy to load the burden of austerity on to low-income families with children?

But last week, Jeremy Corbyn yet again refused to move Labour to a position of unambiguous support for a referendum on any Brexit deal, and a commitment Labour would campaign for Remain, despite the views of the overwhelming majority of party members. And while Labour remains racked by its own Brexit divisions, the Conservatives will continue to evade scrutiny for the damage they seem all too willing to wreak on Britain.