In order to secure the release of an arrested oil tanker, Iran gave a solemn undertaking that it would not be delivering its cargo to Syria. The authorities in Gibraltar, which had detained the Adrian Darya-1, accepted this pledge. Last week, after slow steaming around the Mediterranean, the tanker arrived in Syrian waters off the port city of Tarsus. On Sunday, the foreign ministry in Tehran confirmed the oil had been landed in Syria.

It is hard to think of a more blatant lie or a greater diplomatic insult. For Gibraltar, read the United Kingdom, which at the “request” of the autonomous Gibraltarian authorities, sent Royal Marines to board and stop the tanker as it passed into the Mediterranean. It had loaded its crude in Iran way back in April but had avoided the Suez Canal, sailing slowly instead around the southern tip of Africa in June, as if it were delivering its cargo to somewhere in the Americas.

In response to what it clearly understood to be an initiative from London to enforce the international embargo in the Syrian regime of Bashar Assad, ayatollahs sent Revolutionary Guards to seize a British tanker, the Stena Impero in the Gulf. Until now, it has been standard British policy never to negotiate with hostage-takers under any circumstances. Yet London would doubtless argue that there is a great deal of difference between a British citizen seized by terrorists and a British-flagged tanker, even if it had been seized by what is effectively a terrorist regime.

It is now clear that the British authorities will be furious that they were tricked so conspicuously. The new government of Boris Johnson already has far more pressing issues to consider that cheating ayatollahs, but the long-term effect of the way in which the Iranians lied through their teeth ought to be profound. Until now the UK has been in lockstep with the EU initiative, led by French President Emmanuel Macron, to frustrate Washington’s reimposition of Iranian sanctions. President Trump warned that the Iranians were not to be trusted. He tried to get the government in Gibraltar to hang on to the Adrian Darya-1, which until it reflagged itself as an Iranian vessel while in detention, had been known as the Grace-1. It had been dropped from its original Panamanian registry as part of a raft of measures the US President took to blacklist the vessel and its crew. Moreover, it has been admitted in Washington that before he took these measures, Trump played Mister Nice Guy and authorized that the Indian captain of the vessel Akhilesh Kumar be paid “millions of dollars” to sail his ship into the arms of the US Navy.

It would be interesting to know how much Captain Kumar had been promised by the ayatollahs to press on with his voyage, and more interesting still to know if Tehran actually dishonors this promise as well.

But the real point here is that Iran was very quickly in breach of the 2013 Geneva nuclear deal it signed with the so-easily-duped Barack Obama. EU states refused to admit this and have compounded their error by trying to sabotage the new Trump sanctions. Whatever they may think of this US President, it is now abundantly clear that the venal, incompetent and shifty regime in Tehran simply cannot be trusted.