Britain’s national conversation is subjecting voters to two dangerous falsehoods. The first, that a no-deal Brexit couldn’t harm us. The second, that it could ever happen.

The first fallacy exposes the worst of Brexit’s toxicity: namely, the casual, unabashed exceptionalism that places the enterprising British beyond the laws of gravity. Brexiters protest that our “clean break” departure on WTO rules will ensure that life continues as normal. The only thing that will break in this scenario is Britain’s economy and social contract.

A no-deal Brexit will tear us from every EU law, instrument and agency overnight. We have nothing with which to replace them. Out of the European Aviation Safety Agency, no British plane or pilot will be certified or insured. Out of the single market and customs union, every British lorry will have to be checked at French ports for tariffs and standards, bringing cross-Channel traffic to a standstill. These outcomes are not only legal, but required. The WTO cannot and will not help.

National myth-making may feed our imaginations, but not our stomachs. We are, in reality, not so special

The first falsehood has birthed the second. Persuade enough people that a no-deal won’t amount to an unequivocal national breakdown, and it follows that we may actually end up doing it with public and parliamentary support. But the plan won’t work. We are not leaving without a deal under any circumstances.

First, the political reasons. Chief among them, Theresa May. She will not accept a no-deal scenario. Everything she has done so far demonstrates her terror of it. The EU has called her bluff on the negotiation sequencing, divorce payment, Irish backstop and transition terms, and to keep the show on the road she has blinked each time.

Assume then that May folds and subsequently resigns. The new prime minister declares that no deal really is better than a bad deal. He or she needn’t come clean about the consequences: reality will step into the breach. Put simply, Britain will start shutting up shop by the new year. Tens of thousands of EU citizens will leave, manufacturers will make show-stopping announcements about the closure of businesses, and the pound will tumble. Can the new prime minister depend on voters’ enthusiastic embrace of an entirely voluntary and pointless Blitz spirit, or will they call for a climbdown?

Imagine the political crisis escalates. The prime minister faces down public pressure to change course and has to confront parliament. Which brings us to the other key block for no-deal: parliamentary arithmetic.

Quick Guide What are Brexit options now? Four scenarios Show Staying in the single market and customs union The UK could sign up to all the EU’s rules and regulations, staying in the single market – which provides free movement of goods, services and people – and the customs union, in which EU members agree tariffs on external states. Freedom of movement would continue and the UK would keep paying into the Brussels pot. We would continue to have unfettered access to EU trade, but the pledge to “take back control” of laws, borders and money would not have been fulfilled. This is an unlikely outcome and one that may be possible only by reversing the Brexit decision, after a second referendum or election. The Norway model Britain could follow Norway, which is in the single market, is subject to freedom of movement rules and pays a fee to Brussels – but is outside the customs union. That combination would tie Britain to EU regulations but allow it to sign trade deals of its own. A “Norway-minus” deal is more likely. That would see the UK leave the single market and customs union and end free movement of people. But Britain would align its rules and regulations with Brussels, hoping this would allow a greater degree of market access. The UK would still be subject to EU rules. The Canada deal A comprehensive trade deal like the one handed to Canada would help British traders, as it would lower or eliminate tariffs. But there would be little on offer for the UK services industry. It is a bad outcome for financial services. Such a deal would leave Britain free to diverge from EU rules and regulations but that in turn would lead to border checks and the rise of other “non-tariff barriers” to trade. It would leave Britain free to forge new trade deals with other nations. Many in Brussels see this as a likely outcome, based on Theresa May’s direction so far. No deal Britain leaves with no trade deal, meaning that all trade is governed by World Trade Organization rules. Tariffs would be high, queues at the border long and the Irish border issue severe. In the short term, British aircraft might be unable to fly to some European destinations. The UK would quickly need to establish bilateral agreements to deal with the consequences, but the country would be free to take whatever future direction it wishes. It may need to deregulate to attract international business – a very different future and a lot of disruption.

Tory MPs have so far largely swallowed a hard Brexit they do not want. But a no-deal is an unprecedented catastrophe. Many shy rebels will draw the line at licensing national suicide on principle. Others will think more politically. A Tory government that sends the economy and livelihoods over the cliff will collapse the Tory party for a generation. Even MPs who would not save the country might opt to save themselves. Labour, for its part, declared a no-deal scenario its red line in the 2017 election manifesto. Even a handful of extra Tory rebels would break the government’s Brexit majority. After all, government whips last month threatened MPs that losing a key Brexit vote would trigger a general election, and still only won by six votes.

Why then is May talking up the prospect of no-deal even when it remains inconceivable? This is the real “project fear”. She hopes that just enough talk of stockpiling food and medicine will blackmail just enough MPs into voting for her still-elusive EU deal. Far likelier is that she scares the public into supporting a new vote on Brexit, with the option of abandoning it altogether.

The government and hard Brexiters are really engaging in niche games of cakeism. The government wants to scare us with talk of hardship without spelling out the full horror of no-deal. The Brexit fundamentalists prefer the more traditional Orwellian pursuit of promising no new border controls while simultaneously declaring we will take back control of our borders. The electorate will ultimately punish both sides for their duplicity.

Both the no-deal fallacies originate in the biggest lie of all: that Britain’s putative greatness allows it to defy concrete reality. But in the first instance, we have built our interconnected economic life on the floor of EU agreements that a no-deal instantly cuts away. In the second, we lack the bargaining power, legal security or economic might to legitimise the threat either in Brussels or at home.

Here then is the truth. National myth-making may feed our imaginations, but not our stomachs. We are, in reality, not so special. Any country will burn if you set fire to it. The prime minister may see fit to light the fuse, but so long as we live in a parliamentary democracy, MPs will have the power to confiscate the matches.

• Jonathan Lis is deputy director of the thinktank British Influence