When trouble is brewing at home, populist leaders sometimes find it useful to pick a fight with a foreign neighbour, to whip up patriotic feeling and distract attention from domestic difficulties. This is one possible account of Boris Johnson’s motives for issuing a threat to disregard international law, on the pretext that the European Union side in the current trade negotiations was acting unreasonably and therefore in bad faith. But is he that calculating? It was clear from Monday’s House of Commons debate that the government’s position was full of holes.

The casus belli of this display of diplomatic belligerence was an alleged observation by an EU negotiator that countries outside the EU could only import food into it if they were on the list of countries whose food safety standards were the same as the EU’s or better. Britain certainly fits that criterion now, being still covered by those rules, but has not agreed a set of safety standards for when the rules no longer apply. This has raised suspicions that the UK wants to keep all its options open in trade negotiations with the United States, where standards are definitely lower.