What now with Brexit? Any fool can leave the European Union. You stop going to meetings, cancel the banker’s order and run down the flag. But it will take a diplomatic genius to negotiate a way out of the EU’s customs union and single market and reject Europe’s entire, collective economic area, all in good order and within little over six months. That is the self-appointed task that Boris Johnson’s government has now set itself.

The nation’s departure from the EU this month has been low key, if only because it has made virtually no difference. What now happens — possible disengagement from a maze of commercial and regulatory ties and treaties — could make a big difference, to employers and employees, firms and organisations, farmers, fishermen, financiers and academics.

So-called hard Brexit can be achieved at speed, if no one counts the cost or cares who gets hurt. But that is unlikely to be the case. From money markets to fishing quotas to “third country” food imports, even the hardest deal is political. I know no one close to the Brexit process who regards leaving this year as seriously practicable.

There is one simple and least disruptive path that could be taken, whereby the UK agrees to remain within the existing customs union and single market, with adjustments appropriate to it having left the EU. Boris Johnson showed such pragmatism under force majeur last year over Northern Ireland.

While hard Brexit’s promise of glorious “re-alignment” and “freedom to make deals with the rest of the world” sounds chauvinist and macho, in practice there is no known or proven advantage in it. The sole reason for Johnson opposing Theresa May’s “soft Brexit” deal was to win over the Tory right in his leadership campaign. Now he has won. He can break his promise, as is his wont.

Unless Johnson goes down this path and relents, the prospect re-emerges later this year of no deal, but this time for real. Then the queue of losers will be awesome — car and plane-makers, drugs companies, beef and sheep farmers, drinks and the fashion trade. America cannot and will not possibly compensate.

As for the idea that British traders will become “rule-makers not takers”, that is mere bravado. No one dictates trade terms to Washington or Beijing. Britain could lose between five and fifteen per cent by value of the 40 per cent of its trade that is with the EU, and there is no market anywhere that could compensate for that.

The areas requiring renegotiation — mostly under the single market “freedoms” — are tough enough. They will include fishing quotas, money market regulations, trade arbitration and people movement. Immigration, the only “issue” mentioned by a majority of leave voters, is already vexed, but all Europe is moving towards a debate on this, on migration from outside and within the continent.

Britain needs to be part of that debate, and Johnson has everything to gain by suspending his ban on EU citizen movement until that debate has borne fruit. Upwards of 40 per cent of the British labour force in hospitality, tourism, farming, building and social and health care is made up of EU nationals. The home secretary, Priti Patel, can flippantly tell employers they should train home-grown staff, but she is not an employer. This is not grown-up talk.

A return to another slanging match with the EU’s Michel Barnier, and to more screaming farmers and chaos at the ports, will exasperate a public long fed up with Brexit. There is no yellow brick road to “deals with the rest of the world” and a deregulated Land of Oz. Johnson’s opposition to frictionless trade with the EU will have no traction.

The government’s most sensible strategy is to depoliticise Brexit. Johnson and his allies have made their point and won their battle. He should calm things down, set a compromise agenda and bring the Labour opposition aboard. He must turn a national crusade into a tedious trade agreement. The alternative is a rerun of last year’s no-deal hysteria, followed by a messy climb-down or postponement at the last minute. An island cannot live at odds with its adjacent mainland, especially when there is no good reason to do so. This time Johnson will have no one but himself to blame.

There is nothing new in these tortuous crises in relations with continental Europe. They go back to the seventh-century Synod of Whitby and the battle over whether Britain should ally itself to the Roman church or retain a Celtic aloofness. Britain experienced a successful Norman invasion and an unsuccessful Spanish one. It saw empires built and destroyed, world wars fought and treaties signed. The only constancy has been an apparent craving among Britons for association yet semi-detachment.

Europe’s nation states have themselves tried countless unions, never with much lasting effect. But the present EU, warts and all, has been on balance the most successful. At present such a union is passing through an uncertain phase. Britain has no interest in refusing counsel and friendship to those struggling to hold Europe’s treaties to their original purpose. The least it can now do is pursue its renewed semi-detachment with a softer touch.