In recent weeks there has been intense speculation that in the event of a European Union oil embargo, Iran would try to close the Strait of Hormuz, through which flow 32 per cent of global oil exports and 28 per cent of global liquefied natural gas exports. Such an attempt is unlikely, although, to be clear, history suggests that sanctions would not work in constraining the Iranian regime.

The first reason to believe Iran might stop short of closing the strait is simply because such a move would fail. Cutting off Gulf oil supplies represents an existential threat to the west that it would have to use force to counter. The response, if transit were seriously threatened, would rapidly degenerate into a shooting war between Iran and the US supported by many of its allies. While oil prices might reach unprecedented new levels, the US Navy would quickly restore access.

The second reason is that a serious threat to close Hormuz is arguably the principal Iranian deterrent against a military attack by the US or Israel on its nuclear facilities. So to use it in response to an EU oil embargo would be using that proverbial sledgehammer to crack a pistachio nut.