As every parent knows, family life is all about conflict resolution. Parental authority is a thing of the past, and children know it, so there is no point in demanding obedience. The only way is to work through a quasi-judicial process. When child A wants to watch CBBC while child B wants the Cartoon Network you have to reason with them, and try to establish common rules. Each gets an hour, or the right to use the iPad if they can’t agree which hours to watch. Sometimes it doesn’t work because children are essentially egotists: they don’t understand why they shouldn’t get their way all the time.

International relations are much the same. We no longer have kings and imperial states laying down the law, forcing people to obey. We don’t settle international disputes by war, as countries did almost routinely in the 19th century. We have what is called rule-based international diplomacy: rational laws governing the interactions of nation states. We have rules on human rights like the ECHR, and we have comprehensive trade agreements, like the European Single Market, intended to establish agreed regulations and prevent trade wars. Independent arbitration bodies, like the European Court of Justice, are set up to deal with disputes because if people behave like egotistical children, no-one gets what they want.

Sadly, we appear to be reverting to an era of juvenile international relations, based not on rules, but on might is right. A selfish bigot in the White House, with a big red button, thinks the rule should be “America First”. So he throws his weight around and does things like slapping a 25 per cent tariff on steel imports, triggering a whole series of reactions across the trading networks of which the US is a part. His argument, like that of the older child, is that he is stronger and should get his way. “When we are down $100 billion with a certain country,” Trump tweeted with all the subtlety of a cage-fighter, “and they get cute, don’t trade anymore – we win big. It’s easy!”

Britain tried to do something similar with Brexit. We have the sovereign right to watch CBBC and no-one can take that away from us. We will work with the EU when they want to watch the same programmes as we do, but when there is a difference of opinion, we must have the final say. The court of mum and dad is not an institution we are prepared to recognise when adjudicating on breaches of the rules because this is a child-first approach. And if you don’t like it we’ll take our ball away, so there.

The only problem is that, unlike America, we don’t have a big red button and we are not stronger than everyone else. Coming to terms with this reality has been an uncomfortable experience for the neo-imperialists and English nationalists who have hijacked the UK Government. People like Jacob Rees-Mogg have an essentially 19th-century vision of international relations, based on what used to be called “Splendid Isolation”. Britain didn’t need to bother herself co-operating with the “continent”, or getting involved in their alliances, because we are special. We have the navy, the pound and the Empire on which the sun shall never set. Except that it did. Brexit has been a painful reality check on Britain’s place in a world. No country, not even America, can do splendid isolationism in the era of globalisation. We can’t get our own way all the time, and nor can we make empty threats to leave trading institutions upon which depend the livelihoods of millions of British citizens. The UK approach to Brexit has been like that Blazing Saddles sketch, where the cowboy with the gun pointed to his head says: “We do it my way or I’ll shoot”.

If Theresa May had an ounce of leadership she’d have abandoned hard Brexit long ago and tried to negotiate associate EU membership along the lines of Norway, which means accepting the single market and customs union but rejecting the Common Agricultural Policy and most of the EU’s institutions. Brexit would still be Brexit. There was never any way Britain was going to be able to insist on an arrangement which gives us all the benefits of membership without accepting any of the obligations.

The hard Brexiteers of the Tory European Research Group, and the free market economists supporting them, want Britain to cut ties completely and slash all tariffs unilaterally. Britain would become a low-tax, low-regulation regime like Singapore (which actually is a rather high regulation economy in which 80 per cent of the population live in government-built flats). Pure fantasy. Britain could never have cut itself adrift because all those companies based here, like Japanese car manufacturers and American banks, would be outta here. We’re now in the humiliating position of having to beg to get access to the institutions we abandoned. Those were the “hard facts” May outlined in her Mansion House speech on Friday.

She wants a new Customs Partnership to replace the Customs Union. But what is the difference? She wants Britain to have the right to negotiate independent trade deals while keeping the common tariffs of the Customs Union. Good luck with that. She accepts the City of London will lose its “passporting rights” and that single market access will be difficult for “professional services” – 80 per cent of the UK economy.

So she just invents a unilateral single market in which “all the regulatory standards remain the same”, except in the areas where we don’t want them to. She wants no border in Northern Ireland even as she is busy erecting one. But that’s apparently the EU’s fault. She doesn’t want Canada plus she wants Ukraine plus South Korea – a “multifaceted”, “bespoke” and “tailored approach” giving the UK frictionless access to the single market we just left. We will stay in all the agencies like Euratom and the Aviation Safety Agency because we want to. And we will have “reciprocal and binding commitments” and “mutual recognition of regulations” overseen by the European Court of Justice, whose decisions will be final, except when we don’t want them to be.

At best this was reinventing the wheel: a set of arguments for remaining in trade bodies we reject. But it was shot through with naïve exceptionalism about having our cake and eating it. You can’t behave like this any more, in the family or in the world of diplomacy. Groundhog May has seen the cliff edge and is scrabbling to get back into the security of Europe. But no amount of bluster will conceal the truth: hard Brexit isn’t going to happen as we can’t afford to walk away.