The foreign secretary Boris Johnson made a speech on Wednesday in praise of optimism, confidence and a liberal Brexit. It was rich in rhetorical flourish and almost empty of detail. It was the speech of a politician whose only credibility is as the tribune of the leave campaign, a shameless piece of oration that fell back on his old journalistic trick of describing an EU that does not exist in order to justify his determination to get out. It was billed as an overture to the 48% who wanted to stay in the EU and a definitive speech about the shape of Britain’s future relationships outside it. But it was singularly free of the kind of irksome detail needed to understand a world beyond Europe.

It was rich in what Whitehall describes as optimism bias, “an estimate for a project’s costs, benefits and duration [made] in the absence of robust primary evidence”. It was a Valentine’s Day card to himself and his ambition to be the next Tory leader, an ambition he betrayed with his incoherent answer to a question about whether he would rule out resigning this year.

The Johnsonian version of the EU is a grotesque distortion of reality, like the journalistic copy he once fashioned from banana regulations. As the president of the European commission Jean-Claude Juncker pointed out at a press conference that coincided with the foreign secretary’s speech, no one in Brussels harbours ambitions to build a European federal superstate; if some may once have supposed that the European court of justice could drive the process of harmonisation, for years now its judgments have reflected respect for national courts. Mr Johnson’s pretence that he does not understand the distinction between the jurisdiction of the ECJ over the EU’s charter of fundamental rights, and the entirely distinct European court of human rights in Strasbourg, is simply embarrassing. Even the opaque method of choosing the president of the EU commission, the Spitzenkandidaten process, which Mr Johnson enjoyed mocking, is not some treasured institution but an experiment now under attack from the council itself. The shape of the EU and its future direction are not carved on tablets of stone; they are live and much debated questions in which the UK would once have been fully engaged.

In among the picturesque fantasy it was possible to discern exactly how Mr Johnson wants the Brexit process to develop. Contrary to reports that have emerged ahead of what must be of one of the most briefed speeches of recent times, he denied that he was rejecting a transition or – as he preferred to call it – implementation period. After that period, however, he is determined there should be no obligation to observe EU rules that the UK has not had a voice in shaping. There will be no membership of the single market or the customs union, although he did allow that some harmonisation on manufacturing might be desirable. All this is in line with the prime minister’s own preferred options for the future, set out in her Lancaster House and Florence speeches last year. It is also the absolute minimum position for Mr Johnson, if he is to compete in a future leadership contest against the young pretender, Jacob Rees-Mogg.

What neither the prime minister nor her foreign secretary have yet managed to explain is how the option of an almost complete break with the EU can be accomplished without making a nonsense of the government’s competing obligation to ensure there is no hard border between Northern Ireland and the south. Without an answer to that conundrum, talks about future trade relations will not get very far.

Nor was it a gesture of reconciliation to remain voters. Rather it was the kind of take it or leave it offer that Mr Johnson once imagined would frighten Brussels. That did not go so well, and nor will this. And if it represents the level of debate in cabinet, the eight-hour awayday next week will be just one more round in a dialogue of the deaf. Mr Johnson is sometimes funny and he is clever, both useful attributes for a journalist but not nearly enough to make him even a half-way competent foreign secretary. After a series of missteps, he looks increasingly ill at ease in the public eye. On Wednesday even his jokes fell flat. He has been rumbled.

• This article was amended on 16 February 2018. An earlier version said the European court of human rights was in Luxembourg. It is in Strasbourg.

