Less than four days on, Donald Trump’s war on Iran has sparked global repercussions. The US president and his Israeli allies don’t seem to have planned for more than the devastating decapitation strike on Ayatollah Khamenei and his key advisers.

They assumed that, with their Supreme Leader and top commanders dead, even the hardline Islamic Revolutionary Guards would implode and give up the fight. Instead, often acting on their own initiative (even according to Iran’s foreign minister), the Iranian armed forces have been firing ballistic missiles against their hated enemy Israel, but also swarms of drones – which Iran mass-produces – at the nearby Gulf states.

Worse still, Iran’s remaining proxy militias in Iraq, Lebanon and Yemen’s Houthis are joining the fight as Iran appeals to its fellow Shiite Muslims to rally to its cause. In addition to targeting Israel and American bases, we’ve seen in Bahrain disorder in the streets between the Sunni Muslim monarch’s police and his mainly Shiite subjects.

Iran’s regime might face street protests, too. But there is a split between Trump, who wants a post-war Iran to stay one country and Israel, which has been calling on Iran’s many minorities who make up about 40% of the population to seize their chance to break away from Tehran’s rule.

We now have a multi-layered conflict involving the US and Israeli air forces against Iran’s missiles and drones, but on the ground, armies, militias and even mobs in the streets are beginning to fight each other.

Even if Keir Starmer’s Government wanted to stand aside at first, soon enough the vortex of Middle East war has pulled us in. Trump has made his displeasure with Britain clear because Starmer had refused to let the Americans use air bases on our territory – Fairford and Lakenheath at home, and Diego Garcia in the Indian Ocean. Now, belatedly, Starmer has given in but still refuses to go all in on the US side.

An understandable reason for the Prime Minister’s hesitation is the huge number of British subjects within range of Iranian drones in the Gulf and as far away as Cyprus where our base has been attacked already. Evacuating a third of a million Britons in the expanding war zone to safety would be fiendishly difficult even if airports were not under fire. But “sheltering in place” for many will not be an option. People will want to get back to Britain.

If the Iranian hardliners expand their drone attacks across the Gulf to take out electricity and desalination plants, then life in desert cities will become impossible.

With the RAF involved in “defensive” action against Iranian drones, it will be very risky to use its transport fleet to try to move civilians away. When has the Iranian regime ever shown concern about civilian casualties? But now they might well view an RAF evacuation plane as a target.

Travelling across the Saudi Arabian desert in a convoy of cars and coaches would be far from ideal at the best of times. Under fire it could be murderous. So ex-pats and tourists will have to hope the US-Israeli onslaught on Iran itself stifles the missile and drone launches across the Persian Gulf very soon.

The human drama in the Gulf states is not the only aspect of this war threatening Britain. Iran is lashing out at the Gulf states to disrupt oil and liquefied natural gas exports to America’s allies in Europe. Britain, in particular, has been shutting down its own oil and gas production.

Now, other European states will be competing with us to access alternative energy supplies. That will push up the price of petrol but also electricity because government policy has made us ever more dependent on imports. That was fine in peacetime, but it’s going to prove hugely costly if this war doesn’t stop soon.

Competing for fuel will split Nato allies as each government puts its people first. Such divisions will warm the hearts of our great rival, Russia. Putin’s war chest against Ukraine will be boosted by people buying his oil to replace blocked Middle Eastern supplies.

Britain is woefully prepared for this new war. We have no ground-based anti-missile systems to defend our people abroad in Cyprus or at home – nor enough frigates with anti-missile capabilities at sea. Remedying this will be brutally expensive – especially so in an economic crisis.

And the human cost of war might soon be overshadowed by an economic depression across the West. Every day of fighting makes the prospects grimmer. Expect more unpleasant surprises – for all sides.

Mark Almond is director of the Crisis Research Institute, Oxford