One of the sub-themes of the campaign to leave the EU was that the British fishing industry had been hard done by in four decades of the common fisheries policy. So it is ironic that the current dispute was triggered by an attempt by the Jersey government to ensure that the “fishing effort in our waters is similar to pre-Brexit”.

It is doubly ironic because Jersey never was part of the EU and is not part of the UK. It is a crown dependency that subcontracts its foreign policy to the UK, and so its decision to refuse fishing licences to 75 French vessels has caused a row between the UK and France that has complicated the start of the UN summit on climate change in Glasgow.

Both the French and the British governments have overreacted to a technical dispute – whether those boats can show evidence that they have fished in Jersey waters in the past. Instead of discussing that question, the French have threatened to block British boats from French ports and have hinted at cutting off Jersey’s electricity supply, which comes via undersea cable from French nuclear power stations.

These are not the measures provided for in the Trade and Cooperation Agreement, the treaty signed at the end of last year, in cases of dispute over its interpretation. It contains an arbitration procedure culminating in a three-person tribunal, whose chair and decisive vote could be decided by lot.

So the British government is entitled to suggest that the French should follow those procedures rather than threatening direct action, but the eagerness with which Boris Johnson and David Frost, his Brexit minister, have escalated the war of words suggests that they are happy to use the dispute to their own ends. For all the prime minister’s talk of uniting the country, he seems intent on stirring the endless Brexit argument as a way of keeping Leave voters in his coalition. And Lord Frost seems keen to add the fishing dispute to the list of problems he is discussing with Maros Sefcovic, his opposite number on the joint committee charged with sorting out the post-Brexit relationship, as a way of gaining extra leverage in the negotiations over the Northern Ireland protocol.

Johnson and Frost seem almost gleeful that Jean Castex, the French prime minister, should have blundered in his letter to Ursula von der Leyen, European Commission president, in which he demanded that she “demonstrate to European public opinion that”, among other things, “leaving the union has more disadvantages than remaining within it”.

The translation of his words has become controversial, along predictable Leave-Remain lines, with Johnson’s opponents outraged at his suggestion that Castex was demanding that the EU “punish” Britain for leaving. The key word in the letter was dommages, meaning harms, injuries or merely disadvantages rather than punishments, but the implication of the whole sentence seems to me to be “pour encourager les autres”.

Instead of using Castex’s mistake to present himself as reasonable, however, Johnson chose to respond in kind. After he met Emmanuel Macron on Sunday, the French side said they had agreed to stop arguing. “Oh no we haven’t,” was the pantomime briefing from the British side. The French said the British had agreed to de-escalate the dispute, which would have been a good idea, but the British said it was up to the French to withdraw their unjustified threats.

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Which seems irresponsible at a time when national leaders should be concentrating on more important questions, including the sustainability of all the world’s oceans rather than just the 12 nautical miles around Jersey. Nor does it seem sensible to try to link the dispute over fish in the Channel with the question of the movement of goods to Northern Ireland from the rest of the UK.

On that front it is the British government that is guilty of disproportionate escalation, threatening to suspend the Northern Ireland protocol – albeit under the lawful procedure set out in Article 16 of the protocol – but the situation in Northern Ireland hardly seems to qualify. Article 16 allows either side to suspend the protocol if it leads to “serious economic, societal or environmental difficulties that are liable to persist, or to diversion of trade”. Lord Frost has not explained how those conditions are met, while Sevcovic points out that “not one of the business representatives” he met in Northern Ireland “asked me to scrap the protocol”.

I assume that both Johnson and Macron are posturing for the sake of their respective domestic audiences, but the more they puff themselves up, the more dangerous that game becomes, with the risk of a pragmatic compromise being seen as a humiliation.