Boris Johnson and his predecessor Theresa May surely must be the first British prime ministers ever to leave harbour without a clue where the ship of state will end up.

At least she had a Brexit plan of sorts. But Boris sails on regardless into the high seas, throwing overboard all the lifebelts, sacking key crew, ignoring the rules.

The highest court in Britain, the Supreme Court, ruled unanimously the other week that his prorogation of parliament was unlawful and declared it null and void.

“It didn’t happen,” said Lady Hale, the court’s head, in an elegantly withering judgment.

Parliament had meanwhile passed legislation blocking Boris’s transparent aim of crashing out of the European Union with No Deal – that is without any continued trading or customs relationship with the largest, richest market in the world, responsible for half the UK’s trade in goods and services.

No matter, trumpeted Boris. He wouldn’t be deflected and planned to find a way around the law of the land anyway, determined Britain leaves by 31 October “come what may”.

Women MPs protesting about suffering terrible abuse and even death threats from his militant right-wing followers were indulging in “humbug”.

Buckingham Palace’s displeasure at dragging the queen into his dubious manoeuvres was just another little irritant.

Allegations from reputable sources that Boris favoured a former girlfriend commercially when he was London mayor and intrusively groped a Sunday Times journalist were all just smears by his Brexit enemies.

As for the Supreme Court, it was also simply “wrong”, he insisted. Judges and MPs were “traitors” in a “Zombie Parliament”, his Praetorian guards ranted. Nothing would get in his way of delivering Brexit “on time”.

But he hasn’t been doing very well on that as he pushes forward obstinately, purging Conservative luminaries, losing every key vote in parliament, losing in court, losing his MP brother as a minister and the support of his journalist sister. He faces an investment strike by business, with economic growth rivalling South Africa’s low; the world’s leaders in despair at the fifth-largest economy in the world; and one of the five nuclear power permanent UN Security Council members becoming a laughing stock.

And yet – like his alter ago Donald Trump – Boris sails onward, well ahead of Labour’s dismal opinion poll levels, albeit on a low share of the vote, massively above Jeremy Corbyn in the leader ratings. His right-wing political base loves him: the more he loses votes and judgments, the more he is their hero, standing defiant against these “enemies of the people”.

The majority of big-circulation British newspapers: the Sun, Daily Mail, Daily Express and Daily Telegraph are all echo chambers for his Brexit fervour, and apparently unconcerned that if a Conservative prime minister can behave in this lawless fashion, it might set a precedent for a future left-wing Labour prime minister. In that event, you could safely predict their headline bombast: “RIP British civilisation.” Or “British Stalin.”

For weeks, the prime minister’s EU negotiator was sent to Brussels with nothing to say, nothing to offer, nothing to propose. Yet Boris kept saying, “We’re making real progress”.

Then suddenly, a few days ago, he produced a proposal for the Irish border, always the Achilles heel of hard-line Brexiteers like him. It’s been roundly condemned by Northern Ireland’s road hauliers, businesses, trade unions, and every Northern Ireland political party (including the Ulster Unionists) except his allies the Democratic Unionist Party (DUP).

Unsurprisingly, because it sabotages the all-Ireland economy and betrays the Good Friday Agreement. Both rest upon the foundation of the current open invisible border (like between Limpopo and Gauteng), the whole island of Ireland being in the same European single market and customs union.

His Brexit plan for a separate customs union is unworkable: there are no enforcement measures – leaving it wide open to smuggling and criminality. Because Boris proposes unspecified technology-based “trusted trader schemes” and customs centres somewhere – anywhere – away from the Irish border, his will amount to a virtual hard border, not a physical hard border. In fact, his is a fantasy border.

Except that he is cynically and deliberately passing the parcel to Brussels. The EU will still have to enforce its own rules for customs checks on the Irish side, because Boris’s virtual border won’t be secure: instead an invitation to smuggling and criminality.

After Brexit it will be the external frontier of the European Union. So, much against their will, Brussels and Dublin will have to erect infrastructure for security and checks in order legally to comply with World Trade Organisation rules. Brexiteers will then blame them: “Not me guv,” Boris and his prop the DUP are already saying.

Surely this is the worst of both worlds? Customs clearance checks on the Northern Ireland side. On the Irish side, border security controls that would be a target for civil disobedience and paramilitary attack, and a shift from no borders to up to four borders, because it’s also proposed the island of Ireland, north and south, will continue to obey the same regulations for trade in goods and agri-food. Though even that is subject to a DUP veto the party insisted upon.

Meanwhile, the Irish government – legally and politically equal partners by international treaty in the Good Friday Agreement – has been shunted aside. Trust between Dublin and London – painstakingly built over the last two decades after centuries of British-Irish conflict – has been destroyed.

The tragedy is that this isn’t incompetence. It’s been deliberate. First, running down the clock, then producing with just a few weeks left to the deadline a proposal which neither Brussels nor Dublin could possibly accept.

The outcome: what his hard-line followers and Nigel Farage really want, hoping to make it a complete break with the EU. Their wider aim is to convert Britain into a free-for-all, deregulated and fundamentally unequal country, blissfully disengaged from its European neighbours where high social standards and equal rights are just as important as economic competitiveness.

Amid all the noise, drama and shredding of convention and decency, it’s easy to forget what Boris and his Brexiteers are really doing.

Nearly 50 years of progressively intimately integrated trade, economic, social, environmental, human rights, defence and security relationships with Britain’s closest neighbours are just being torn up. And even worse, without any alternatives being put in their place.

The current Boris mantra is “Get Brexit over and done with”. It won’t be. This is just the beginning of a monumental act of national self-harm.

And why? Because his favoured No Deal marks just the start of years – maybe 10 years on precedent – of tortuous negotiations to establish proper trade agreements. Not only with Britain’s 27 European neighbours, but also with 70-odd other countries (from South Africa to Japan) with which we currently have such agreements, through – and negotiated by – the European Union.

Early signs are not encouraging for Boris. Asked by the government to roll over the EU’s recent free trade agreement with Japan – to which London through Brussels is a party – Tokyo refused. Why? Because the Japanese had had to make concessions to Europe’s 500 million market that it doesn’t need to for Britain’s 65 million one.

Even if Boris unexpectedly compromised and got a deal, that would still just be the start of similarly long years of trade negotiations, except with the comfort of a transitional arrangement maintaining the status quo for a few years, where No Deal means crashing out with a hard landing.

Because, in the end, the Brexiteers have promised the impossible: keeping all the benefits of being in the European Club without any of the obligations.

“Take back control!” was their slogan. “Losing control” will be their outcome.

In my Daily Maverick Opinionista piece a month ago I wrote of the Brexit saga: “it’s going to get worse”.

It did.

And it still will. DM