Should Britain consider independent actions to seize sanctioned tankers?
The Big Ask | No. 02.2026
Last week, the United States (US) seized the Marinera, a Russian-flagged oil tanker in the North Atlantic. Formerly sailing as the Bella 1 under Guyanese flagging, the Marinera has historically been used to transport crude oil from Venezuela – an associate of the so-called ‘CRINK’ nations of the People’s Republic of China (PRC), Russia, Iran and North Korea.
The United Kingdom (UK) aided the US in seizing the ‘shadow fleet’ vessel by providing Royal Air Force (RAF) surveillance aircraft and support from RFA Tideforce, thus demonstrating the will to act against adversaries and protect its own interests. Taking this to its next logical step, for this week’s Big Ask, we asked five experts: Should Britain consider independent actions to seize sanctioned tankers?
Political Adviser to the Commander, NATO MARCOM
Should the UK consider independent actions to seize sanctioned tankers?
Yes and no. The question begs a number of critical questions. To begin with, all maritime interdiction action is independent, in that Britain will be liable for its actions both legally and strategically, regardless of whether it is responding to an American or North Atlantic Treaty Organisation (NATO) request, or conducting interdiction as an independent policy.
The second consideration is the focus on action against sanctioned tankers, which is both overbroad and too narrow. The shadow fleet is propping up the Kremlin’s full-scale invasion of Ukraine. Some elements of it are flying false flags, and thus stateless and without insurance. Others are ‘Flag of Convenience’ vessels, often with substandard insurance and of poor seaworthiness. An increasing number are now legitimately Russian-flagged; others claim to be.
Their sanctioned status may be fixed, or may flex with the market price relative to Group of Seven (G7) caps. Nothing stops the UK from seizing stateless tankers nor those where the flag registration process was irregular, whether on the high seas or national waters. Indeed, Britain should do so to support Ukraine and uphold international law at sea.
At present, this still applies to the bulk of the shadow fleet, as well as legitimately flagged tankers – of whatever nationality, including Russian – under sanction which enter territorial waters other than for transit. Seizure creates several challenges – where will these ships be berthed, what will become of them, and who will pay for it?
The benefits to freedom of navigation and to Ukraine should trump these concerns. However, national sanctions alone do not create a right of high seas enforcement on legitimately foreign-flagged shipping. That is a diplomatic state to state matter. Such action would be highly escalatory, legally being in the wrong and providing a damaging precedent.
The hard case comes when a stateless, sanctioned tanker is being escorted by a Russian warship. On legal and escalatory grounds, it is more prudent to consider the ship under Russian sovereign protection (and liability). Yet, short of that hard case, Britain should act where statelessness and sanctioned status coincide. In fact, it should act on statelessness alone to the extent it can.
*This response is written in a personal capacity, and does not necessarily reflect any official national views, nor those of NATO.
British Defence Attaché to Ukraine (2008-2011) and Russia (2019-2022)
Despite the American seizure of the Marinera, the shadow fleet of decrepit, inadequately insured and poorly crewed tankers used by Russia to transport oil remains a significant challenge. Sanctions have not prevented the fleet from expanding to perhaps 20% of the global tanker total. Dozens of shadow fleet vessels have sailed through the UK’s Exclusive Economic Zone (EEZ) since the detention of the Marinera.
After four years of conflict, British politicians are belatedly talking tough about further enforcement action. Yvette Cooper, Foreign Secretary, promised to ‘tighten the chokehold’ further, while John Healey, Secretary of State for Defence, said that ‘deterring, disrupting and degrading’ the fleet is a priority for His Majesty’s (HM) Government. A legal mechanism to authorise boardings and detentions of unflagged or improperly flagged vessels has been identified.
Britain should seriously consider further boarding operations in home waters. The strategic benefits – upholding sanctions, disrupting funding of Russia’s aggression against Ukraine, diverting the proceeds of illegal oil to Ukraine, protecting the environment, safeguarding critical underwater infrastructure and reducing danger to commercial shipping – outweigh the risks of Russian retaliation, international unease and legal challenge.
The UK’s boarding operations are unlikely to cause significant dents to the shadow fleet alone. Expansion of the use of boarding should be coordinated with allies; unilateral bravado would be unhelpful. Coordinated expansion of British, American and European Union (EU) sanctions against the shadow fleet is also required, together with a blanket ban on maritime services – including shipping, insurance, crewing and operations – on any ship transporting Russian carbon-based energy resources. This approach should also be extended to the export of Russian fertilisers; another big export earner for the Kremlin.
Professor of International Security and Co-Director of Security Research Institute, Lancaster University, and Visiting Fellow, Royal Navy Strategic Studies Centre
Boarding commercial vessels on the high seas without consent – even when justified under United Nations Convention on the Law of the Sea (UNCLOS) exceptions such as ‘statelessness’ – carries significant legal, diplomatic and political risks. Indeed, such actions challenge established norms and practices and can escalate tensions. Yet, risks can be offset by potential benefits, such as reducing shadow fleet activity and improving the enforcement of sanctions.
Whether the use of force can effectively deter shadow fleet operations remains highly uncertain. These vessels operate within a well-entrenched business model, driven by owners and captains willing to profit from illicit and opaque practices. These networks are supported by adversarial states such as Russia and Iran, and facilitated by permissive buyers and open registries which reinforce opacity and limit regulatory oversight.
So far, this has limited the success of sanctions enforcement. Now, the use of force against contravening civilian vessels could demonstrate resolve, and thus help deter shadow fleet operators by denying the use of UNCLOS as a shield for sanctions evasion.
For HM Government, this can also contribute to posturing and strategic deterrence against Russia’s broader malign activities at sea. Yet, it might also reinforce power politics at sea by undermining UNCLOS, paving the way for expanded hybrid warfare in the maritime domain.
Ultimately, rather than deterring Russia, this could incentivise the Kremlin to escalate sub-threshold activities without even maintaining plausible deniability, signalling a shift toward more overt and aggressive ‘grey zone’ operations which further destabilise the maritime domain.
For HM Government, the risks and benefits of seizing sanctioned tankers must be carefully weighed, as such decisions carry strategic and legal implications alongside the potential gains in deterrence and sanctions enforcement.
Adjunct Fellow, Council on Geostrategy, and Associate Fellow, Royal Navy Strategic Studies Centre
Against the backdrop of the British Armed Forces supporting the seizure of the Marinera, recent discussions have focused on the future use of British special forces to seize and detain ‘stateless’ vessels. Whether the UK should act independently depends on its willingness to own the responsibility and consequences if, or when, it chooses to do so. Ultimately, a strong case can be made for boarding and seizing stateless vessels, as inaction risks normalising sanctions evasion, but it is not without its challenges.
Intervening in another state’s trade is inherently delicate, and independent direct action would require naval resources that Britain currently lacks. Coordinated action with allies or partners would better manage risk. However, even where a vessel can credibly be deemed stateless – justifying a seizure under international law – challenges remain. The Baltic states, for example, have grappled with the practical question of what such enforcement should look like and what should follow from such action for a while now.
Current discussions highlight the reality of maritime security: the law of the sea is largely shaped by precedent where there is ambiguity, leaving room for interpretation. In the current climate, whether an activity is formally illegal feels secondary to what states believe they can get away with. While some warn of countermeasures, the UK’s adversaries are already pushing boundaries, raising the question of what protection caution really offers when only one side abides by international law.
Adjunct Fellow, Council on Geostrategy, and Professor of War and Strategy in East Asia in the Department of War Studies, King’s College London
The question is deceptively simple. It is hard to resist the temptation to suggest that Britain should indeed consider independent action to seize sanctioned tankers. From the perspective of both capabilities and precedent, the UK would stand on solid ground to do so.
Almost two decades of persistent counterpiracy and interdiction activities from the Caribbean to the Indian Ocean have enabled Britain – and, in fairness, many other European powers – to possess a fine set of capabilities to board and secure suspicious vessels. In terms of precedent, the recent intervention by French special forces to seize the stateless ship Boracay set an important standard for other countries, including the UK, to follow.
Yet, the question is not one of capabilities, but rather of political opportunity. In this respect, the key question is whether independent British action would bring greater value than concerted action with other allies and partners. Within the context of how shadow fleet assets are empowering the Russian military machine, the issue is not merely a British problem. It is about European security and, as such, there is a genuine advantage in working with others to pursue such an objective.
HM Government has already indicated as much, and allies are seemingly interested in exploring options. Such a choice has a clear operational advantage, and offers an opportunity to contain potential risks. The operational advantage is that concerted action makes it harder for suspicious vessels and their masters in Moscow to know when, and from where, action will be taken towards them. From a risk perspective, collective action makes it harder to identify proportionate targets for responses, keeping the calculus of how to respond to such actions more complex.
In all, yes – the UK has probably considered independent action, but political leaders have also probably considered that working with others is a more desirable option – which does not preclude, in the future, to consider options to go alone.
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