Iran’s main tactic in the crisis over sanctions and Gulf shipping is to divide the opposition, keep them guessing, and prepare to operate over a broad front, and not just in and around the Straits of Hormuz. The long-term aim of those who rule the Islamic Republic is harder to discern. At the moment it appears to be geared at little more than strategic survival.

For Iran these are desperate times. The super-sanctions imposed by Donald Trump on withdrawing from the nuclear deal, the Joint Common Plan of Action of 2015, are really hurting in terms of prices, inflation, and food shortages for many Iranians. Iran wants to keep the JCPOA going, if the European signatories will help. But above all it needs to sell oil.

Just over a year ago some 2,450,000 barrels of Iranian oil passed east through the Straits of Hormuz each day. Now it is around a tenth of that.

Commitments in Syria, the support of Lebanese and Syrian Hezbollah, material and assistance for the Houthis in Yemen are an additional burden. Payments for Hezbollah widows’ pensions and compensation of wounded Hezbollah veterans are a drain on cash reserves.

Yet they have a couple of strategic advantages. First, for all the belligerent huffing and puffing of John Bolton, the national security adviser, and the two Mikes – Pompeo and Pence, the cheerleaders of the militant Evangelical wing at the White House – it is clear Trump himself does not want war. In fact, those now organizing his re-election campaign are suggesting a drawn-out conflict with Iran, along the lines of the recent US commitments to Iraq and Afghanistan, could wreck altogether the chances of a second term.

Iran was also given a boost when a party of British Royal Marines seized the Panama registered Grace 1 off Gibraltar on 4th July. Allegedly, Grace 1 was in breach of EU sanctions against Assad’s Syria in carrying a cargo of nearly two million barrels of Iranian crude to be refined at Banias on the Syrian coast.

Not too much has been said by the EU about sanctions up to this point – but the UK says it was working with Gibraltar to enforce them. The unfortunate twist is that it was all done on an American tip-off; and the tanker had been tracked by US surveillance since it left the Gulf and made the round trip into the Mediterranean via the Cape.

Iran has sensed that the UK is the weak link, diplomatically stranded between Europe and the US, whose posture on the post JCPOA super-sanctions it opposes. Iran called the Grace 1 seizure “piracy.” The Tehran foreign ministry spokesman Abbas Mousavi warned me in an exchange on Al Mayadeen, the pro-Syrian and Iranian tv station in Beirut: “We will take a British ship. We will strike in the Gulf and maybe elsewhere.”

And so they did, first trying to grab the tanker British Heritage and then seizing the Stena Impero, now impounded in Bandra Abbas with its crew of 23.

The British appear overwhelmed, undermanned and ill prepared. The Iranians have struck in the dog days of an interregnum between prime ministers. The Royal Navy has only one major warship in the area, the ageing Type 23 frigate HMS Montrose. She is to be relieved, to go into local refit, by the destroyer HMS Duncan, super-modern with the world-beating Sampson radar. But the entire class of six Type 45 destroyers needs a major overhaul. Because of a critical design fault, they cannot operate in high heat – like that in the Gulf now.

As things stand, Iran and the Revolutionary Guard Corps are more than capable of holding their own. They are highly skilled at opportunist raiding with small attack boats, helicopters, drones and small submersibles, both manned and unmanned, and frogmen. They arranged the attack on six tankers in six weeks – with munitions of Iranian manufacture – and just about got away with it.

They know how to stir things up on a number of fronts. Not only can they threaten the Straits of Hormuz, the main choke point on the Gulf, but their allies of the Houthi guerrillas of Yemen, and further south the Al Shebab of Somalia threaten another choke point on the Red Sea at the Bab Al Mandeb. The Al Shebab, Houthis and allies, now have a string of raiding bases in little pirate ports up and down the coast from the Red Sea through Puntland and down to the Horn of Africa.

In Lebanon and Syria Iran is reinforcing Hezbollah with new weaponry. Israelis have been regaled this week with unsubstantiated tales of Iran mounting major resupply operations to Lebanon and Syria by sea.

Israel is a wild card – and it may not play to Iran’s advantage. With the chances of re-election on 17th September getting slimmer by the week for Binyamin Netanyahu, he is sure to ramp up the bellicose rhetoric against the Islamic republic. If the war-party in the White House try to match him, the odds will shorten substantially on a big military accident in the Gulf region sometime soon.

But this isn’t just a story of Iran and the West. About a fifth of the world’s maritime trade in oil, and a third in liquid gas, pass through the Straits of Hormuz each day. Most of it goes east not west, to India, Japan and China. Those in charge in Iran, and the Guards, the clerics and the politicians – who are surprisingly united for the moment – know this is perhaps their strongest suit.