France’s interior minister, Gérald Darmanin, is a sensitive soul. He dislikes British politicians saying nice things to him in private, then turning round and using “insulting” and “strongly unfriendly” language in the House of Commons and the press. He is particularly upset by his British opposite number, Priti Patel, and her boss, Boris Johnson, doing this on the topic of immigration. We might wonder where the French minister spent his political upbringing to become so innocent of political reality. Yet the substance of Darmanin’s complaint is true. The current cross-Channel migration crisis has two dimensions. One is the real human anguish needing diplomatic and practical resolution. The other is its exploitation in a shouting match for public and political consumption. Thousands of refugees have sought British shores this past year, and last week tragedy struck as 27 of them died in the crossing. It was more than Johnson could stand. The tragedy made a mockery of his boast that Brexit would allow him to “take back control” of immigration. In response he duly wrote to the French president, Emmanuel Macron, with his proposals for ending the cross-Channel migration, couched as virtual demands. They included the stationing of British forces on French soil and the immediate return of people back to France. He must have known they were unacceptable. Bizarrely, Johnson released his letter on Twitter before it was even delivered through diplomatic channels. Its message was clearly intended for the British public rather than the Élysée Palace, and it could hardly have been better crafted to infuriate the latter. Macron’s response to the Channel tragedy had been to summon an emergency meeting of EU migration ministers to Calais. The predictable outcome of Johnson’s letter was that Priti Patel was disinvited from the meeting. With Britain’s interest excluded, the ministers merely insisted that any solution to ongoing European migration should be EU-based not bilateral Anglo-French. So much for Johnson’s demands. Why Johnson should have wanted to sabotage the Calais meeting is a mystery. It suggests a complete lack of discipline or competence in Downing Street and, we must assume, a collapse of liaison with the Foreign Office, which would normally vet such a letter and cannot conceivably have approved it. The prime minister’s obsession with his daily photographs and macho press releases is not a route to effective government, least of all during this sort of diplomatic standoff. Britain is moving towards an ever more disadvantageous relationship with the rest of Europe, on migration as on other facets of the single market. Brexit has not, as Johnson bragged, made it stronger, but made it weaker. That does not mean it is ineffective. It remains a force on the European scene. But it needs friends and allies and should tread with care. Europe must urgently find a way forward in an era of persistent migration that does not respect national borders – because it is unlikely to cease in the near future. Johnson should suspend his Brexit bombast and join the EU in handling this predicament. He should look for solutions, not headlines. Just now he has a particular need to find them in collusion with France. So what is the point in being rude to Macron? Simon Jenkins is a Guardian columnist