Next week the Bulletin of the Atomic Scientists will unveil the current time on its Doomsday Clock, meant to convey the nuclear dangers facing the world. The closer the clock is to midnight, the greater the existential threat. If the stand-off between Iran and Donald Trump persists, or takes a frightening turn for the worse, then the clock’s hands may be closer to the bell tolling than they have ever been. This would mean the danger to the planet was judged greater than at any time since the first H-bomb tests.

The drumbeat of war reverberates around the Middle East. On Tuesday, Britain, France and Germany said that they had been “left with no choice” but to trigger a dispute mechanism in the six-nation nuclear deal with Iran after Tehran declared, in the aftermath of the US assassination of its top general, that it would no longer observe the pact’s “operational restrictions”. Iran’s president then warned that European soldiers in the Middle East “could be in danger”, a clear indication that if the continent stood with Mr Trump then its forces could expect to be treated as enemy combatants.

Europe, including Britain, must not follow the folly of President Trump’s strategy. Last year he pulled out of the nuclear deal saying it was not working when it was. He then gambled that crippling economic sanctions would bring down Tehran’s regime. That has not paid off. Rather Iran has lashed out with a series of audacious strikes against Sunni Arab rivals and western targets. It began slowly walking away from the nuclear deal. The Iranian regime’s downing of an airline, and then lying about its responsibility for that tragic error, has elicited, rightly, public fury. It is hard to tell whether this anger will be channelled into a wider movement that threatens the regime. Mr Trump now appears to be recklessly speeding towards war with Iran. Europe needs to apply a brake.

At the heart of the 2015 nuclear pact was a simple quid pro quo: Iran agreed to constraints and inspections in exchange for the financial benefits of sanctions relief. It is important to note that the European move opens a 30-day window for talks to see if differences can be bridged. If still unresolved then the matter could be brought before the United Nations’ security council, raising the spectre of the return of sanctions lifted under the deal. Mr Trump might relish the prospect of Iran being dragged before the UN. He should not. Without a ladder to climb down, Tehran may go for broke. If Iran resumes the parts of its nuclear programme it mothballed, or, even worse, if it ends international inspections, the world could see Iran racing to get a bomb. It is ironic that such a dilemma, when faced five years ago, led to the Iranian nuclear deal.

Richard Goldberg, a former Trump adviser, made it clear the US president is unlikely to forgive an isolated Britain, especially one desperately looking for a trade deal, if it takes a stance over Iran at odds with America. Boris Johnson has sought to flatter by promoting a “Trump deal” with Iran. There is a logic to this even if it looks like rewarding belligerence. Analysts say Mr Trump campaigned to bring US troops home and that is what the Iranian regime wants too. Could the price be Iran giving up its pursuit of a nuclear arsenal along with sanctions being lifted? To get Iran back to the negotiating table would require clipping the wings of US hawks. Under the current circumstances the chances for talks are slim. But if the old deal cannot be rebuilt or a new one struck, then the choice will be to allow Iran to get the bomb or to bomb Iran. Then we will be very close to midnight.