They cannot be serious. The UK Government is to issue 70 “technical notices” in the next few weeks advising families and small businesses on how to prepare for a no-deal Brexit. You know, stuff like stock-piling canned food and medicines in case of dislocation at the ports. Firms to start making customs declarations for the first time, and to prepare for the abrupt departure of EU staff. We'll no doubt be told to assist the army guarding the ports and help the police prevent any civil disobedience from three million-odd EU citizens who’ll be left high and dry. Oh, and forget air travel, continental holidays, mobile phone roaming. Not so much Project Fear as Protect and Survive.

Of course it will never happen. It's all Remoaner fantasies and Brussels scaremongering to try to get Britain to submit to the heel of the European Court of Justice and cough up the £40 billion divorce bill. Except that this scaremongering isn't coming from Brussels, but from the British civil service whose job it is make contingencies. And they are right to do so. A no-deal Brexit is looking more and more likely, following the effective demise of Theresa May’s compromise White Paper last week.

Her attempt to remain in the EU regulatory environment by adopting a “common rule book” – in other words, agreeing to replicate all the terms of our current membership while not actually being a member of the EU – pleased no one. It was condemned as “vassalage” by Boris Johnson in his resignation speech, and a “national humiliation” even by pro-Europeans like the former Labour EU Commissioner, Lord Mandelson. The trade bills scraped through parliament last week on the back of a handful of rebel Labour MPs and the indolence of the current and former Liberal Democrat leaders who failed to show for a crucial vote on Monday. But amendments from hard Brexiteers have made May’s White Paper unworkable.

The Scottish Government hasn't commented on the no deal preparations, but it, too, will have to think the unthinkable. This week the Supreme Court will rule on whether the Scottish parliament had the right to pass a Continuity Bill, seeking to retain control over devolved powers like food, fishing and environment repatriated from Brussels. But this has been comprehensively overtaken by events. The Scottish Parliament was reduced to the status of a parish council last week by legislation that ran roughshod over Holyrood's legal right to withhold consent if it disagrees with aspects of the new trade agreements. No Sewel convention is going to prevent Scotland disappearing down the Brexit sink hole.

Now, when people talk of a no-deal Brexit they usually mean something like Britain “reverting” to World Trade Organisation terms, or a Canada-style free trade agreement. Wrong. No deal means no deal – it means no trade agreement, no two-year transition period in which things remain largely as they do today. No rights to travel in Europe for work or leisure without a visa, no common standards for medicines, nuclear material or air safety. Everyone will do their best to prevent relations with Europe breaking down completely, and people being hurt – but accidents can happen.

A no deal would be Britain’s biggest economic dislocation since the Second World War. Even a bog standard, free trade deal has to be negotiated and the one struck last week between the EU and Japan took eight years. And even when we have one, it will not be anything like Britain's current “friction-free” access to the customs union and the single market. There will be tariffs of 10 per cent on cars (so goodbye Nissan and Honda) and 15 per cent on average on food. But much worse will be all the non-tariff barriers to trade: like sanitary and “phytosanitary" regulations [protective measures against contaminants] which could make much produce unsellable. Service industries, which make up 80 per cent of the British economy will find that they are not automatically authorised to trade in the EU. Banks and financial services will lose their “passporting rights” – though many have already jumped ship.

There will be a hard border in Ireland, or the Irish Sea, because there has to be one, despite what Theresa May said in Ireland last week. No dealers, like the Tory MP John Redwood, insist this is not necessary. “We don't want to set up any borders” he says.

This is a new dimension in post-truth politics verging on the theatre of the absurd. The whole point about Brexit was to set up borders – that is what leaving the European Union means. And the UK's only land border with Europe runs right through the Emerald Isle. It’s 500 km long and has 300-odd crossing points. Moreover the Good Friday Agreement requires regulatory harmonisation north and south. Brexiteers seem to believe that everything will just continue as it does now, and that all those multilateral agreements Britain has entered into over the last 40 years will somehow still apply even as we leave the EU.

Right wing economists like Professor Patrick Minford insist that Britain will be so efficient, freed from Brussels red tape, and so low cost, that we we’ll still be able to flood their markets with our cheap goods and services. But that kind of Vietnamisation of the UK economy is not something that British people are quite prepared for. Brexiteers expect the “anglosphere” – the Commonwealth plus America – to give preferential terms to the UK. But countries like Canada and India are all much more interested in trade deals with the EU, not their former imperial master.

Remain-voting Scotland has been watching the slide to a no deal Brexit with mounting alarm. There was chaos in Westminster last week, as pairing arrangements were abandoned, Tory anti-Brexit rebels were threatened, and a clutch of die-hard pro-Brexit Labour MPs saved the day for Theresa May. It felt like being chained to a lunatic. Every constituency in Scotland voted to remain and the consequences of a no-deal Brexit for Scotland will be dire.

But not nearly as dire as it will be for the future of the United Kingdom.

Descent into no-deal chaos, or even the imminent threat of such, will surely lead to the collapse of the UK Government. Theresa May has been a “dead woman walking”, to use the former Chancellor’s phrase, for over a year, and now she isn’t even doing that. With parliament deadlocked, and both the major UK parties opposed to a repeat referendum on Brexit, her departure should mean a General Election, as the Tory party spirals into a state of civil war.

In any General Election against the background of a no deal Brexit we can expect the SNP to return another super-landslide even greater than in 2015. Labour will be condemned for failing to defend the Scottish Parliament's powers, and for Jeremy Corbyn's refusal even to contemplate a soft Brexit solution involving continued membership of the customs union and single market. The Scottish Tory revival is already stone dead, and the Liberal Democrats are irrelevant. Scots will vote with fury for the party that has consistently opposed Brexit: the SNP. That could mean curtains for the Union, as Scots realise that they made a mistake in 2014. The Tory right better believe it: no deal means no more UK.