No deal is one of those really bad ideas, like shell suits or Celine Dion, which we thought we could leave in the past. But this summer it's somehow all the rage. It's discussed as if it were just another Brexit option.

It is not. No-deal is probably the most demented policy put forward by mainstream British politicians in the modern era. To see how it would work in practice, this piece looks at what would happen on day one. Doing this for the whole economy would take countless pages of Stephen-King-style horror, so it's stripped down to one topic: food. This is the story of how our system for importing and exporting food implodes almost instantly.

You may remember 'Brexit means Brexit' - that nursery rhyme from the bygone days of late 2016. It was false. But no-deal, on the other hand, really does mean no-deal. The withdrawal treaty comes as one package, so if Theresa May fails to secure it, everything falls down. There are no deals on anything.

March 30th 2019 becomes Year Zero. Overnight, British meat products cannot be imported into the EU. To bring these types of goods in, they have to come from a country with an approved national body whose facilities have been certified by the EU. But there has been no deal, so there's no approval.

This sounds insane. After all, British food was OK to enter Europe with minimal checks on March 29th, so why not on March 30? Nothing has changed.

The reason is that food is potentially very dangerous, so we have strict systems in place for it. Imagine that right now someone is eating a burger made from the meat of a cow with a neurodegenerative disease, like BSE. This is what happened in Britain in the late-80s and led to the deaths of 177 people. Tomorrow's tabloid front pages will ask certain very important questions. Where did the meat come from? Was it produced domestically or imported? Who was responsible for its production, transport and storage? The people responsible will be hauled in front of cameras and Commons select committees. Ministers will have to give statements to parliament. The press will demand that heads roll.

The BSE outbreak almost brought down the government. That's how severe these threats are. And there are plenty more around, including foot and mouth, avian flu, and African swine fever, plus those that do not exist yet.

This is why the certification system for food coming into Europe is so stringent and detailed. After Brexit, we will fall out of the eco-system of EU rules, agencies and courts and become an external country. That means certification requirements will apply to us too.

Certificates are approval stamps, designed per product and country, documenting the fact that it meets the various standards for human health and animal welfare. Say a container full of pork loins is sent from Leeds to Amsterdam after Brexit day. It will need to be signed off by a vet to say that the meat was slaughtered, stored, quality assured, sealed and despatched in a certain manner, with appropriate documentation proving compliance.

This will be a cold splash of water to the face for Britain. We've grown so used to frictionless EU trade that our food system is based on something called Just In Time. The idea behind this is that products are constantly cycling from producers to consumers, without being stored in big cargo holds. It's more efficient and also more pleasant. This is why you eat fresh tomatoes from countries miles away without ever really having to think about how extraordinary it is. Under your feet, a miraculous logistical engine is constantly pumping ham and cheese and fruit and veg and bread around the continent. It's a circulatory system of yummy wonderfulness.

2/ @IanDunt on the 'modern day miracle' of Just-in-Time (JiT) inventory systems that we all secretly take for granted, when we visit the supermarket. #skypapers pic.twitter.com/t4feiNn6BP — Martin Cooper (@mpc_1968) July 26, 2018

The UK is particularly reliant on Just in Time because it doesn't feed itself. Domestic food production has been steadily declining from the early 1980s and is now at just 60%. Most of our imports come from the EU because it is closest to us. With food more than arguably any other good, distance is important - because it'll go off. About 10,000 containers of food come into the UK from the EU daily. (This is an excellent recent report on Britain's food security and its vulnerabilities.)

But the efficiency makes it fragile. The impact of no-deal Brexit on this system would be an implosion in the trade network. Suddenly, the full certification system would need to be checked at the border. Frictionless trade would be replaced by standard-issue bureaucracy.

This is where the crunch point will be. The main ports affected will be the ones at Dover, Calais, the Eurotunnel, Dunkirk, and Holyhead, for trade to and from Ireland.

Products of animal origin from non-EU states must pass through special border inspection posts, manned by a vet. Calais and the Eurotunnel are not equipped for this. Dunkirk is, but it has a very low capacity.

We have a very significant infrastructure problem here. We don't have enough inspection posts, we don't have the staff to man them, we don't have the means to divert product to them and we don't have the cold storage capacity to handle product going in and out. Many ports don't have space to install more facilities.

Inspections take time. Where a product must be detained and a sample taken off for testing, the process can last around 36 hours.

It is fatal. A study by an expert on traffic modelling from Imperial College London earlier this year found that if the current average paperwork clearance of two minutes at Dover was increased to just four, there would be a 20-mile tailback within 24 hours on the UK side. This would balloon as the days wore on.

It doesn't really matter which side the tailbacks start on - European or British. One side affects the other because there is limited space for goods to move. Some experts predict a total breakdown of the Just In Time system by day five. That's where the horror stories you read about stockpiling come from. Very quickly, we'd see empty supermarket shelves.

At this point, Downing Street could decide to unilaterally give up all these tests and procedures for goods coming into the UK. After all, it is now unbound from EU law. It can do what it likes.

There is some evidence that this is what ministers are planning. In February, Defra minister George Eustice told a Lords committee his department would implement a 'mutual recognition' regime, which ultimately amounts to assuming food from the EU was safe to eat and hoping they did the same. Transport secretary Chris Grayling told the BBC categorically in March that "we will not impose checks" at the port of Dover.

But this approach would have profound consequences. Overnight, there would be no protections whatsoever for UK consumers on the food they eat.

This would be a betrayal of ministers' assurances of high food standards after Brexit, but put aside the morality and think about the practicality. Opening the border in this way would provide an open invitation for fraudsters. They could send anything to the UK they like - any food product, any drink, with any ingredient - knowing there would be no checks. The spot check system operating under EU law would vanish. There would be no documentation, no safeguards, no court oversight, and no supervision.

The UK would be instantly downgraded to pariah status by the EU and the rest of our trading partners. British food exports would shrivel up.

The other solution would be to turn away from the continent and start importing our food from across the Atlantic.

The problem with this idea is the existence of geography. The EU is not our main food supplier because of some metropolitan conspiracy by people who like brie. It's our main food supplier because it is close to us. The US, regardless of its 'Anglophone' cultural credentials, is further away. US exports to the UK are proportionately tiny. They are ranked 10th, behind a host of European countries. For America to replace this volume of trade flow in nine months is simply not realistic. No-one with any understanding of the industry thinks it is possible.

But ministers like Liam Fox will likely demand this anyway - not because it makes sense, but because it provides them with a historic and irreversible opportunity to break Britain away from the continent and towards the US.

This is because of something called 'sanitary and phytosanitary standards'. These are global measures to protect people, animals and the environment from diseases. The EU has one approach to these and the US has another.

Years ago Nasa developed something called Hazard Analysis and Critical Control Points (HACCP). It was an extremely systematic approach to guaranteeing quality control on foods, primarily for the reason that it is very, very problematic if an astronaut gets diarrhoea. The EU adopted this very high standard in 2006.

The US, on the other hand, has much lower standards. The EU rejects US standards on the levels of pesticides residue in fruit, for instance, hormone injections in beef and chlorine wash for poultry. It has strict and very welcome requirements on the excess and routine use of antimicrobials in agriculture. Anyone who has had their life saved by antibiotics will recognise why this is sensible long-term rule-making.

Brexiters pretend post-Brexit Britain will forge its own standards in trade, but that is false. We're a medium-sized country surrounded on both sides by massive trading entities. The reality is we'll either snuggle into the EU ecosystem or the US ecosystem - it's as simple as that. On food, this is basically about which set of sanitary and phytosanitary standards we adopt.

If Brexiters can force a situation - especially in the chaotic furnace of no-deal - where the UK starts de-facto accepting US standards by having to bring in lots of their food, it makes it harder for us to align with the EU again in the future. It's a fait accompli, except that Fox would consider that phrase unforgivably continental. Maybe he'd prefer Mission Accomplished.

As the days and weeks wore on after a no-deal Brexit, British agriculture would be pulverised.

Tariffs are exorbitantly high for food products. Under a deal, they'd be kept at zero, but without one they'll average 22%. This would devastate UK agricultural exports, whose main market is Europe.

Britain could decide to unilaterally bring these tariffs down to zero. But you can't discriminate between countries under World Trade Organisation (WTO) rules, so it would then have to do this for the rest of the world as well. That would bring in a flood of cheaper agricultural products from countries with lower standards and protections.

Food prices would come down for some consumers. This would force domestic British agriculture consumption into a death spiral. They'd be blocked from exporting to their largest foreign market and suddenly faced with impossible competition at home.

Alternately, the UK could try to move past the immediate chaos of no-deal, pull itself together, and level-up capacity so it could get the certification system demanded by the EU up and running. But here it runs into another problem, which feels disturbingly like the twist at the end of a morality tale: there aren’t enough vets, because they're all from the EU.

British vets like setting up small clinics in a village somewhere and saving the family dog. Admit it. That's the image in your head when someone says the word 'vet'. They do not envision spending their career watching cow carcasses being washed down in an abattoir. The culture of veterinary checks in food is much more common in Europe, especially in Spain. EU citizens consequently make up 95% of the veterinary workforce in UK food production.

If Britain is going to suddenly have to do all these checks to export food to the EU, it will require a massive increase in these types of vets. But at the moment we can't even keep the ones we've got. European workers are leaving, sick of the lack of security about their status and a national conversation which only ever treats them as a problem. We lose about 20 EU vets a month from the sector.

Without a deal on Brexit, it becomes hard to fill that gap, because new EU workers would find it harder to come to the UK. This hinges on something called 'mutual recognition of professional qualifications'. If there's a deal, the qualification you have in Europe entitles you to work in the UK and vice versa. If there isn't, all that falls down.

This is the scale of the catastrophe no-deal entails. And this is just one area. It does not cover what would happen to services, or industrial goods, or the fact planes would be grounded, or energy, or any other part of the economy. This is just one sliver of the chaos which would hit the UK. There are simply no precedents for this scenario.

It remains, even now, unlikely that it would happen. No advanced country has committed hara-kiri like this. The weeks leading up to no-deal would likely see a form of market panic. Once investors decided it was really going to happen - say late January or mid-February - they would act accordingly.

That would sharpen minds in London and Brussels. Some kind of emergency provision would probably be passed. This would not be a deal. It would be a sticking plaster saying existing UK-EU arrangements on trade are carried over past Brexit Day for a limited period.

This would prevent catastrophe, but not for long. It would probably be a matter of weeks.

So even in this best-case no-deal scenario, things would be very intense. Britain would have to make crucial decisions about its future very quickly. That core issue in the Brexit debate - do we pick the EU ecosystem or the US one - would suddenly have to be dealt with. It would be a decision made to a razor-sharp timetable, amid scenes of extraordinary political chaos, with consequences that would define the economic future of the country.

We'd be fiddling, while drunk and hysterical, with the levers of the country's engine room. And we would make mistakes: long-term, core-function errors under impossibly volatile conditions.

No matter how soothingly they suggest it, this is not something any rational person would want. The fact we are even talking about it suggests there is something deeply wrong with us.

This piece is based on conversations with…

Jason Aldiss, managing director of Eville & Jones, a leading provider of official veterinary controls, and former president of the Veterinary Public Health Association.

Tim Lang, professor of food policy at City University London

Tony Lewis, head of policy at the Chartered Institute of Environmental Health

Sam Lowe, senior research fellow at the Centre for European Reform and visiting research fellow at the King's University Policy Unit

...and several others in London and Brussels who chose not to be named.

Ian Dunt is editor of Politics.co.uk and the author of Brexit: What The Hell Happens Now?

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.