British Crusade to the "Shadow Fleet"
Prelude
On January 7, 2026, the US Coast Guard seized the Marinera, a Russian-flagged tanker transporting Venezuelan oil. The operation took place in the waters between Iceland and Scotland, after a pursuit lasting over two weeks, and was conducted with British surveillance assistance. It had nothing to do with Russia’s so-called “shadow fleet”, being instead tied to the enforcement of Washington’s oil embargo against Venezuela. Still, the seizure of a Russian-flagged tanker and the muted reaction from Moscow reopened the talks about seizing the vessels of the “shadow fleet”.
Britain has been one of the most radical actors of the Ukrainian crisis on the Western side. While Washington has mostly focused on strengthening the “New Iron Curtain” along the Gdansk–Constanta line, just west of Russia’s “Red Line”, Britain’s position was way more advanced, as shown by the 2021 Black Sea Incident. This stance hardened after February 24, 2022; the role played by Boris Johnson in sabotaging the Russo-Ukrainian peace talks in April 2022 is well documented, and it did not change much even after the Labour Party replaced the Conservatives in the 2024 election.
Therefore, Britain has taken a leading role in the fight against the “shadow fleet”. The country has sanctioned 544 of these vessels, and in 2025 it created a mechanism to monitor the vessels through the Joint Expeditionary Force (henceforth JEF), a British-led military partnership with the Scandinavian countries, the Baltic ones and the Netherlands. Likewise, in December 2024, the UK reached an agreement with Denmark, Sweden, Finland, Poland and Estonia to require proof of insurance from vessels transiting through the Baltic Sea.
The cooperation in this sector is particularly strong with Denmark, since it holds most of the keys to the Baltic Sea. Although the Danish Straits are international waterways as per the 1857 Copenhagen Convention, monitoring and even blocking them would not be difficult for Copenhagen, and we should not be surprised that Denmark alone has identified 292 tankers by February 2026.
This list has made it harder to sell Russian oil above the West-imposed price cap; but Russia continues to do so, albeit at a discount. On February 26, 2026, for instance, the Urals benchmark was $57.84, around $10 below the other benchmarks ($70.84 for Brent, $65.21 for WTI), but still well above the $44.10 cap imposed by London and Brussels. This left the fight against the “shadow fleet” at an impasse. The next step is the seizure of the tankers; but such an option faces several challenges, especially if done on a massive scale.
Legal Challenges
Like the seizure of Russian sovereign assets, seizing the vessels of the “shadow fleet” poses many legal challenges. True, the definition of “piracy” by the United Nations Convention on the Law of the Sea (henceforth UNCLOS) covers only the seizure of vessels for private ends, with no mention of state-related ones. But the convention was signed in 1982, and while piracy is still an occurrence in some parts of the world, state and state-sponsored piracy were part of a bygone era.
This vacuum, nevertheless, does not imply that seizing such vessels would be legal. Unlike UN sanctions, which are binding for all UN states, Western sanctions are not valid outside their jurisdictions, and UNCLOS states that ships of all countries enjoy the right of innocent passage through a country’s territorial sea, or transit passage through a strait used for international navigation.
This issue already emerged in 2019, when Britain seized an Iranian oil tanker transiting through Gibraltar’s territorial waters. The vessel, according to British authorities, was headed to Syria, then under Western sanctions. Iran retaliated by seizing a UK-registered one in the Strait of Hormuz.
The legality of both seizures is dubious. UNCLOS states that countries may limit the right to innocent passage in order to ensure the safety of navigation, the protection of living resources and of the environment. This, nevertheless, did not apply to the Iranian tanker, while Tehran’s claims that the British tanker could collide with an Iranian fishing vessel could not be verified independently. At the same time, the accusations of “state piracy” Britain and Iran hurled at one another had a mostly political and rhetorical value, given the lack of such a definition in UNCLOS.
The aforementioned crisis is indicative of the potential legal challenges around a campaign against the “shadow fleet”. The British government has been looking for a legal justification for such a crusade, for instance by appealing to the 2018 Sanctions and Money Laundering Act, but its soundness remains questionable, since third countries are not bound by non-UN sanctions and applying these sanctions in spite of the right to innocent passage may be perceived as an act of war. The 2019 crisis did not escalate into a wider one because it was solved after a few months, when both seized vessels were released.
A Challenge of Narrative
The challenges are not only legal, but also narrative. First advanced in 1609 by the Dutch lawyer and philosopher Hugo Grotius, the idea that the sea can be used by everyone to trade with anyone without limitation has become a main tenet of the branch of Western civilization that came to dominate it. In 1994, almost 400 years after the publication of Mare Liberum, the idea of freedom of navigation was codified by UNCLOS, and this convention further developed the idea of mare liberum, for example by introducing the right of innocent passage through another country’s territorial waters which is now common practice in international navigation.
Since freedom of navigation is a main tenet of the Western liberal global order, the negation of this right to a country the West does not like would represent a further blow to its perceived legitimacy, especially in the eyes of non-Westerners. Already in 1996, at the heyday of US hegemony, the American political scientist Samuel P. Huntington famously wrote that “hypocrisy, double standards and ‘but nots’ are the price of universalist pretensions”, criticizing the self-evident divergence between the principles proclaimed by Western countries and their actual policies. In the ongoing transition towards a multipolar world, these accusations would resound even louder.
France’s Moves: Britain’s Brain?
The Boracay Precedent
This did not stop some countries from acting against the “shadow fleet”. The first instance was the seizure of the Boracay, a Benin-flagged vessel captured by France in September 2025. Although part of the “shadow fleet”, the official reason for its seizure was its supposed involvement in a drone incident. Given the lack of proof, the Boracay was released on October 2, 2025, five days later; still, this move was a testing ground for more decisive action. And, in December 2025, the EU capitals drafted a joint interpretation of UNCLOS to allow the seizure of such vessels.
The Mediterranean Wave
This prepared the ground for more overt moves in the following months. On January 22, 2026, the French Navy took the Grinch, a vessel carrying Russian oil from Murmansk. The seizure took place in international waters between Spain and Morocco. The official reason is the use of a flag of convenience—a controversial but still common practice in the seafaring industry—but Macron’s announcement clearly signaled the actual reasons. The vessel was released on February 17, 2026, upon payment of a fine, but the crusade was now on.
A second vessel was seized in international waters during a joint French-Belgian operation on March 1, 2026, and a third one, the Deyna, was seized on March 20, 2026, while sailing off the coast of Algeria. Finally, on April 3, 2026, the Swedish Coast Guard took a tanker sailing from Ust-Luga off its southern coast, the official reason being a possible oil spill.
Britain Steps Up, Sort Of
What is Britain’s role in this crusade? On March 25, 2026, it stepped up its involvement. Starmer authorized the British Army to interdict vessels of the “shadow fleet” transiting UK waters, although under strict caveats. Yet, unlike France and Sweden, Britain has not taken any direct action so far. Its strategy is mostly one of buck-passing, monitoring Russian vessels passing nearby and providing intelligence for seizures carried out by others, from the aforementioned Marinera to the Grinch and the Deyna. But this may change.
Towards a Kinetic Conflict?
The point of the seizures is to apply maximum pressure on Moscow without facing retaliation. But this cannot last forever. The crusade against the “shadow fleet” is, after all, a sort of chicken game. If Russia does not react, or cannot prevent further seizures, Western governments will feel emboldened and start taking more aggressive steps. But if Russia does act, these governments face two choices: back off, thereby suffering the same loss of credibility Russia would face by inaction; or fight back, with unforeseeable consequences.
Moscow’s Incremental Response
Russia has adopted an incremental response, originally just diplomatic. Following the seizure of the Boracay, Putin accused France of “state piracy”. The harsh rebuff of two Macron advisers who recently visited the Kremlin to press for a role in the Ukraine peace talks is not officially related to the seizures, but the French Navy’s activities clearly did not help.
And, on March 18, 2026, the President of the Maritime Collegium Nikolai Patrushev announced measures to protect Russian trade by deploying military vessels, one of which was recently detected in the English Channel.
No Face to Save
Will this be enough to stop the Western campaign? Facing a Russian military vessel, the countries taking part in the crusade would have the same two choices: back off, or fight back. The latter is the most dangerous, especially if it produces casualties or material damage. But the former amounts to a loss of face, which can ultimately force these countries to step up anyway.
It should be noted that Britain and Russia tend to look down on each other. For the former, Russia is a rogue state to be contained by any means; for the latter, Britain is a sanctimonious second-rate power incapable of much without Washington’s help. Under such conditions, there is little either can do just to save face.
The Iran War: An Elephant in the Room
There is, nevertheless, an elephant in the room which could prevent this from happening: the Iran War. The outbreak of the war on February 28, 2026, caused not only a spike in oil prices, but also the closure of the previous gap between the Urals benchmark and the Brent and WTI ones.
The tighter supply pushed Washington to issue a waiver on the sanctions against Russian oil, recently renewed, while Brussels postponed a ban on Russian oil imports, previously due from 2027, without setting a new deadline. It even funded the reinstatement of the Druzhba pipeline, despite earlier rows with Slovakia and Hungary over their continued imports. Even the truce has not reversed this trend so far, with the Urals benchmark trading almost $30 above the Brent and WTI equivalents on the day the ceasefire was announced.
Is the campaign against the “shadow fleet” still feasible? Apparently, yes, as shown by Macron’s harsh statement announcing the capture of the Deyna. But the tensions in the Persian Gulf, the higher oil prices, and the deployment of military vessels to defend the Russian tankers have tilted the balance in Russia’s favor. While the rest of the world watches the Middle East with concern, direct action against the “shadow fleet” and the Russian vessels protecting it may prove highly unpopular with Western public opinion, especially given the course of the campaign against a much weaker opponent like Iran. And since the Gulf may remain unstable for months, the case for the crusade may only weaken further.
