European leaders responded in strikingly different ways to the stunning news of the assassination of Qassem Suleimani in an American drone strike on Baghdad airport on January 3. The French president, Emmanuel Macron, phoned his counterpart Barham Salih, to assure him of support for the “security and sovereignty” of Iraq.

Boris Johnson, Britain’s newly re-elected prime minister, continued his New Year holiday on the private Caribbean island of Mustique with his girlfriend, uncharacteristically saying nothing for two days until arriving home and declaring that "we will not lament his death."

The European Union’s foreign affairs chief Josep Borrell called on all involved "to exercise maximum restraint and show responsibility at this crucial moment." Germany sent a similar message, prompting criticism by the US Secretary of State Mike Pompeo who said: "Frankly, the Europeans haven't been as helpful as I wish that they could be."

The UK foreign secretary, Dominic Raab, echoed the EU line – and confirmed that he would be going to see Pompeo on a previously-arranged visit to Washington. Raab claimed the US had the right to self-defence in the face of the “menace” represented by Suleimani. But when he said that “we understand the action they took” it fell far short of a ringing endorsement. Britain, which has 400 troops in Iraq training local security forces, was not consulted about the drone attack.

The US and Europe, are, however, divided by far more than the Baghdad assassination. On paper, all EU member states remain committed to the 2015 nuclear agreement (JCPoA) with Iran, were alarmed by President Donald Trump’s decision to abandon it in 2018 and opposed his policy of “maximum pressure” on Tehran. Whatever they said publicly to avoid upsetting the Americans, the pre-meditated killing of Suleimani was certainly seen privately as a risky and reckless act without any accompanying strategy.

Iran and allies like Hizbullah issued various threats in the wake of the assassination, but the first substantive announcement from Tehran was that it would no longer be bound by the restrictions on uranium enrichment in the JCPoA. The chances are that they might well have taken that step anyway – in protest against the continuing European failure to find ways to build a bartering system to circumvent unilaterally re-imposed US sanctions.

But the decision is likely to lead, sooner or later, to the total collapse of the agreement. In the words of one diplomat, it is already “a candle that is burning from both ends.” Sanctions relief, desperately sought by an Iranian government that has seen serious protests in recent months, seems further away than ever.

The Europeans’ problem with Trump is his combination of inconsistency and volatility. His failure to respond to repeated Iranian provocations in the Gulf reflected reluctance to expose US armed forces to danger. The biggest of these was the lack of retaliation for the September drone and missile attack on the Abqaiq oil installation in Saudi Arabia – despite boasting from the Oval Office that US forces were “locked and loaded.”

More recently, Europeans were angered by the president’s decision to withdraw US forces from northern Syria and approve an offensive by Turkey against the Kurdish fighters who had spearheaded the defeat of Isis (Daesh) . That was seen as empowering Turkey, Iran and Russia – and by extension President Bashar al-Assad. It is Europe, far more than America, that will likely pay the price of a resurgent Isis emboldened by the American pullout.

Now something similar may be under way in Iraq following the decision of the Baghdad parliament to formally end the presence of foreign forces and the suspension of operations by the anti-Isis coalition. That raises the possibility that having targeted the shadowy mastermind of Iran’s growing regional hegemony, Trump could now end the US military presence in Iraq completely – 17 years after the overthrow of Saddam Hussein.

The danger of Iranian retaliation for the Suleimani killing has already generated nervousness. Within hours the UK defence secretary Ben Wallace announced that two Royal Navy vessels will again accompany UK-flagged ships through the Straits of Hormuz, as they did between July and November last year following the seizure of a British-flagged tanker by Iran. In the UK Suleimani’s death is also a blow to hopes for the early release of Nazanin Zaghari-Radcliffe, the British-Iranian dual national who was falsely imprisoned in Tehran on charges of espionage.

Britain is still divided and distracted by the looming reality of Brexit – now formally taking place at the end of January. But Johnson is likely to try to work together with the French and Germans – the grouping known as the E3 – in order to soften the diplomatic impact of leaving the EU and, more importantly, to open up a wider channel of communication with Washington at a time when matters in the Middle East look likely to become even more complicated.

Ian is a former Middle East editor, diplomatic editor and European editor for the Guardian newspaper. In recent years he has reported and commented extensively on the Arab uprisings and their aftermath in Syria, Libya and Egypt, along with frequent visits to Iran, the Gulf and across the MENA region. His latest book, a new history of the Palestine–Israel conflict, was published in 2017 to mark the centenary of the Balfour Declaration and the 50th anniversary of the 1967 war. He has an MA in history and social and political science from the University of Cambridge and a PhD in government from LSE. Ian has written for the Economist, the Washington Post and many other publications, and is a regular commentator on TV and radio on Middle Eastern and international affairs. He wrote the introduction to The Arab Spring: Revolution, Rebellion and a New World Order (Guardian Books, 2012); Israel's Secret Wars (Grove Press, 1991), Zionism and the Arabs, 1936–1939 (Taylor & Francis, 1986, 2015); and contributed to the Encyclopedia of the Modern Middle East and North Africa (Macmillan Library Reference, 2004). His most recent book is Enemies and Neighbours: Arabs and Jews in Palestine and Israel, 1917-2017 (Allen Lane, 2017).