On July 4, a team of around 30 British Royal Marines were deployed to Gibraltar to help detain supertanker Grace 1 believed to be carrying two million barrels of crude oil to the Baniyas Refinery in Syria in violation of European Union sanctions against the Assad government, a major ally of Iran’s.

The incident took place against a backdrop of a simmering dispute on Tehran’s retaliatory breach of the nuclear accord—officially known as the Joint Comprehensive Plan of Action (JCPOA)—and how European powers should redeem it in the face of the Trump administration’s “maximum pressure” campaign against the Islamic Republic. The confiscation was reportedly carried out at the behest of the United States and warmly welcomed by the US National Security Advisor John Bolton as “excellent news.” 

Deeply in the throes of leaving the EU, Britain is unsurprisingly trying to warm up to the US and its regional Arab allies such as Saudi Arabia and the United Arab Emirates, which it will have to rely further on economically and politically in the post-Brexit era, by being so-called “tough” on Iran. 

Yet, given the strained European silence on the issue, including by France and Germany—both signatories to the nuclear agreement—the tanker seizure seems to have been interpreted in Tehran as a signal to the Iranian leadership that Europe is willing and ready to overlook its differences with the US and join Washington’s pursuit of crippling pressure on Iran if it carries through with threats of nuclear escalation.

In an alarming reaction to the incident, Mohsen Rezaee, Secretary of Iran’s Expediency Council and a Revolutionary Guards commander, warned in a tweet that “if Britain does not release the Iranian oil tanker, it is the authorities’ duty to seize a British oil tanker.” 

The threat of reprisal was reinforced the following day by Mohammad Ali Mousavi Jazayeri, a member of the Assembly of Experts—a clerical body in charge of overseeing the Supreme Leader and choosing his successor—who stressed that Britain should be “scared” of Tehran’s retaliatory measures over the “illegal” seizure of the supertanker. 

A few days later, on July 11, the UK government announced that a Royal Navy warship had staved off three Revolutionary Guards speedboats trying to block a British-owned tanker passing through the Strait of Hormuz between the Persian Gulf and the Sea of Oman.

The detention of Grace 1 has put Tehran in a difficult position. 

The seizure of a British oil tanker in retaliation could spark a diplomatic crisis between Iran and the European Union and push the latter closer towards the United States at a time when the Islamic Republic needs European help to keep its economy afloat. More specifically, it can adversely affect European tolerance of Iran’s gradual reduction of nuclear commitments under the JCPOA in response to US sanctions.     

Iranian inaction, on the other hand, runs the risk of prompting a so-called domino effect and encouraging Tehran’s other nemeses to follow suit and try to enforce American or European sanctions against it in the high seas. 

Public suspicion and sensitivity about the UK in Iran do not help either. The incident has revived bitter historical memories of a British-American coup in 1953 against Prime Minister Mohammad Mosaddegh who nationalized the Iranian oil industry at the expense of Britain. The Persian-speaking social media have been awash with calls for retaliatory measures against British interests until London is forced to release the confiscated oil tanker.

Diplomatic efforts to defuse tensions have so far failed to yield substantial results.

Diplomatic efforts to defuse tensions have so far failed to yield substantial results. UK Foreign Secretary Jeremy Hunt, who is also a Tory leadership contender, has offered to return the tanker in exchange for guarantees that its massive oil cargo not be delivered to Syria. Iranian Foreign Minister Mohammad Javad Zarif has denied the allegation, insisting that Grace 1 was headed to a legal destination in the eastern Mediterranean Sea. 

Either as a result of British lobbying to ease tensions or for fear of regional escalation and its grave security consequences, some of Iran’s neighbors seem to be adopting a more conciliatory stance. On July 15, Tidewater Middle East Co., Iran’s largest port operator, declared that Kuwait had released a major Iranian crane vesselArvand Tide 1000—10 months after it was detained at the Kuwaiti Port of Shuaiba over “baseless allegations.” Iranian Oil Minister Bijan Zanganeh has also told lawmakers in Tehran that the faceoff with the UK could be resolved through diplomacy, suggesting that retribution is not necessary. 

Ayatollah Khamenei warned that the Islamic Republic and its “devout elements will not leave vicious Britain’s piracy unanswered.”

On Tuesday, Iran’s Supreme Leader Ayatollah Khamenei warned that the Islamic Republic and its “devout elements will not leave vicious Britain’s piracy unanswered.” The menacing rhetoric is reminiscent of a mob attack on the UK embassy in Tehran by a group of pro-state plainclothes hardliners who were indignant at London’s “anti-Iran” policies over its nuclear program. 

Yet, Tehran will likely try to use the Gibraltar incident as a source of political leverage to increase pressure on the EU and compel it into shielding Iran’s economy against US nuclear sanctions. But if push comes to shove, and European powers resort to punitive measures to coerce Iranian nuclear compliance, Tehran might very well respond by seizing the assets of its adversaries or a repeat of sabotage attacks on international shipping in the Gulf.