The UK-Iran contretemps over tankers is not really about legal right and wrong. Rather it is about politics and power. But given that international law is often used to advance national interests, it is useful to examine the respective legal arguments.
On 6 July, police and customs agents from the British Overseas Territory of Gibraltar assisted by British Royal Marines seized a supposedly Panamanian-flagged supertanker—the Grace 1–off its coast.
The legal justification for that seizure is questionable. The UK said that the vessel was carrying Iranian oil to Syria in violation of the European Union’s (EU) sanctions on Syria. https://www.reuters.com/article/us-mideast-iran-defence-minister/irans-defense-minister-says-britains-seizure-of-oil-tanker-was-threatening-act-idUSKCN1U30CQ Iran has denied the oil was destined for Syria. https://www.bbc.com/news/48977093 Moreover some question whether or not the sanctions apply to other than EU members.
https://www.washingtonpost.com/world/middle_east/british-marines-seize-tanker-suspected-of-carrying-iranian-oil-bound-for-syria/2019/07/04/681458d2-9e65-11e9-83e3-45fded8e8d2e_story.html?utm_term=.c11dedb58c61 Perhaps more important, Iran and many others do not recognize the EU sanctions because they have not been endorsed by the UN Security Council.
A more worrying issue is the applicable navigational regime in the area of the seizure and whether or not that regime was violated by the UK action. According to legal expert Don Rothwell, “the transit passage regime applies throughout the entire strait including through the territorial sea generated offshore to Gibraltar”. https://opil.ouplaw.com/view/10.1093/law:epil/9780199231690/law-9780199231690-e1172 Transit passage means the exercise of navigation and over flight solely for the purpose of continuous and expeditious transit of the strait. Transit passage cannot be impeded, hampered or suspended. If the vessel was in transit passage, then the U.K. has violated the law of the sea. https://www.un.org/depts/los/convention_agreements/convention_overview_convention.htm
The seizure has had unintended international consequences. According to the U.K., on 19 July “Iranian authorities seized the British-flagged vessel, Stena Impero in Omani waters in clear contravention of international law. (https:www.gov.uk/government/news/foreign-secretary-statement-on-iranian-actions-in-the-strait-of-hormuz) It was then forced to sail into Iranian waters. https://www.gov.uk/government/news/maritime-security-in-the-gulf-uk-government-response UK flagged shipping through the Strait of Hormuz essentially ground to a halt. https://www.albawaba.com/news/pm-may-holds-talks-gibraltar-chief-minister-about-iranian-owned-oil-tanker-1298036 until Britain started to escort its flagged vessels. https://www.reuters.com/article/us-mideast-iran-britain/britain-begins-escorting-all-uk-vessels-through-hormuz-strait-idUSKCN1UK1HI
Then UK Foreign Minister Jeremy Hunt said the incident amounted to “an act of state piracy.” This is a non-sequitur. According to the UN Convention on the Law of the Sea (UNCLOS), piracy is an illegal act committed for private ends by a private ship outside the jurisdiction of any State. This was an act by a state. The Iranian Navy seized the tanker at the request of the Ports and Maritime Organization of Iran’s Hormozgan province. Moreover it was not for “private ends” and it took place in waters under Omani and Iranian jurisdiction. However as with the UK seizure of the Iranian tanker, it might be state sponsored terrorism or grand theft. That remains to be officially alleged, investigated and proven or disproven—in both cases.
According to Iran’s Foreign Minister Javad Zarif tweet “_ _ our action in the Persian Gulf is to uphold int’l maritime rules – – it is IRAN that guarantees the security of the Persian Gulf & the Strait of Hormuz. U.K. must cease being an accessory to #Economic Terrorism of the U.S. https://www.aninews.in/news/world/middle-east/uk-must-cease-being-accessory-to-us-economic-terrorism-says-iran-fm20190720214550/ Iran said the ship was entering the Strait from the exit point in the South, “disregarding the established procedures that require all entries be made through the Northern pass.” https://www.cnn.com/middleeast/live-news/iran-british-tanker-july-2019/h_6fd50f81a1120ed526085a1a0519ef3a It also had turned off its GPS tracker and thus posed a grave danger to other vessels. https://www.cnn.com/middleeast/live-news/iran-british-tanker-july-2019/h_d7e3aad4250e50e4359544af9c78f8ef If so this would be like a runaway double semi-trailer truck going the wrong way on a major highway with its lights off.
The tanker was apparently diverted by Iranian forces in Omani territorial waters for security reasons. https://theconversation.com/iran-what-the-law-of-the-sea-says-about-detaining-foreign-ships-in-transit-120816 Both Oman and Iran claim that only the regime of innocent passage—not transit passage– applies in the Strait of Hormuz. According to UNCLOS which both Oman and the UK have ratified—but Iran has not– “Innocent passage is innocent so long as it is not prejudicial to peace, good order or security of the coastal state.” To paraphrase the key provisions of this section of the Convention, the coastal state may adopt laws and regulations in conformity with the Convention and international law relating to innocent passage through the territorial sea for the safety of navigation and the regulation of maritime traffic such as sea lanes and traffic separation scheme. “Foreign ships exercising innocent passage “shall comply with all such laws and regulations _ _.” The coastal state may take necessary steps in its territorial sea to prevent passage which is not innocent. So if the ship was violating the traffic separation scheme and endangering other vessels then it would be legal to “prevent its passage.” https://www.cnn.com/middleeast/live-news/iran-british-tanker-july-2019/h_e8b3fd04461b127220d59e9284462503
However there are several problems with this construct.
First of all, the U.K. maintains that the forced diversion occurred in Omani waters. Unless Oman asked or gave permission to Iran to undertake the action, Iran had no right to act unilaterally and use the threat of force.
Second, the coastal state cannot discriminate in form or in fact among foreign ships. But Iran has indicated that the detention of a UK tanker was a “reciprocal” act for the detention of its tanker by the U.K. There is legal doctrine of countermeasures but making that argument would tacitly admit that its own actions were probably unlawful and amounted to discrimination against UK vessels..
Third, if Iran is exercising criminal jurisdiction for violations of its laws or international laws by the ship and its crew, it has to show that the consequences of the crime extend to it (such as the striking of one of its flagged fishing boats) or that it ‘disturbed the good order of its territorial sea’. Moreover, it must immediately notify a diplomatic agent of the coastal state. It is not clear that Iran satisfied all these conditions.
Finally there is the question of legal standing to make these arguments. So far the only clear legal link with Iran is that it owned the cargo. It may or may not own the vessel and its flag is unknown since Panama had removed it from its register.
More important, the U.K. claims that the transit passage regime applies in the Strait As in the Strait of Gibraltar, transit passage cannot be hampered, impeded or suspended. A question is whether attempted passage in violation of a traffic separation scheme is “continuous and expeditious” as the transit passage regime requires.
The seemingly tit-for tat seizures come in the context of the US withdrawal from the 2015 nuclear accord and its unilateral imposition of sanctions on Iran. Indeed, the UK seizure of the Iranian tanker was allegedly undertaken at the request of the U.S. although both the UK and the US deny it. https://www.theguardian.com/world/2019/jul/05/spain-to-lodge-complaint-over-british-seizure-of-oil-tanker-gibraltar Whether true or not, to Iran and some others, the UK action is an effort by a group of nations to circumvent the UN and make new international law by state practice. They believe it should be opposed by those who purport to support the “existing international order.”
The legal arguments justifying both seizures are muddled and weak. International law is unlikely to resolve this issue. But it may play a role in negotiations. Nevertheless it would seem that an old-fashioned horse trade –a swap of tanker releases–may be the way out of a dangerous situation for all concerned.