Downing Street confirmed that British forces will now be able to interdict vessels linked to Russia’s ‘shadow fleet’ in British waters, following a meeting between the UK Prime Minister and Finland’s Prime Minister Petteri Orpo on Thursday 26 March 2026 in Helsinki during the Joint Expeditionary Force (JEF) leaders’ gathering. Both leaders underlined the need to sustain pressure on Russia. The UK also set out an ambition for a closer relationship with the European Union. (gov.uk)
The term ‘shadow fleet’ refers to a network of largely older tankers and associated support ships that seek to evade G7 and EU sanctions on Russian hydrocarbons, often operating with opaque ownership, complex flagging and high-risk practices. The UK has progressively escalated action against this activity, including announcing plans to sanction up to 100 tankers in 2025, and has backed Nordic‑Baltic efforts calling for coordinated measures against vessels not carrying a valid flag in the Baltic and North seas. (gov.uk)
The domestic legal framework enabling interdiction rests on the Sanctions and Anti‑Money Laundering Act 2018 and the Russia (Sanctions) (EU Exit) Regulations 2019, as strengthened by the 2022 No. 203 amendment. These measures allow the Secretary of State to ‘specify’ individual ships suspected of sanctions circumvention and to issue port barring, movement and detention directions. Crucially, detention can occur at a UK port or anchorage, and UK registration can be refused or terminated for specified vessels. (legislation.gov.uk)
At sea, interdiction of foreign‑flagged ships in UK territorial waters engages the maritime enforcement powers introduced by the Policing and Crime Act 2017. Under the statutory Code of Practice, a law enforcement officer may act where there are reasonable grounds to suspect an offence triable in England and Wales, with authority from the Secretary of State required for actions against foreign ships. Royal Navy Police have been designated with enforcement powers to support such operations where deployment of civilian police is impractical. (gov.uk)
International law considerations remain central. Nordic‑Baltic governments have flagged action ‘within international law’ against vessels failing to fly a valid flag in the Baltic and North seas-an issue that can render a ship effectively stateless and subject to boarding. The UK’s approach, set out in recent government statements, explicitly aligns interdiction with the rules‑based order and collective action with partners. (gov.uk)
In practical terms, ‘British waters’ means UK internal waters and the territorial sea. Interdiction will typically involve surveillance and identification, challenge by the Royal Navy or other authorised officers, and direction to a UK anchorage or port for inspection and potential detention under sanctions regulations. The government has also linked interdiction to JEF activity, including the ‘Nordic Warden’ system monitoring 22 areas of interest across the North Sea, English Channel, Kattegat and Baltic, coordinated from Northwood. (legislation.gov.uk)
Legal coordination with partners has been active this month. On 11 March 2026, the Defence Secretary and the Attorney General convened JEF nations’ legal representatives to work towards a shared understanding of the legal basis for countering shadow‑fleet activity, including options for military action consistent with international law. (gov.uk)
European precedents underscore what interdiction may involve. In February, French authorities detained the Comorian‑flagged tanker Grinch, suspected of shadow‑fleet ties, and released it after a multimillion‑euro penalty and weeks of immobilisation. In January, the United States seized the Russian‑flagged Marinera between Iceland and Scotland, with UK assistance; ministers described the operation as compliant with international law. (apnews.com)
For ports, insurers and service providers, UK guidance clarifies that enforcement responsibilities sit with the Department for Business and Trade (trade sanctions) and the Department for Transport (shipping sanctions). Draft 2026 Port State Control guidance proposes strengthened reporting of anomalies by harbour authorities and pilots, reinforcing the pipeline from interdiction to inspection, detention and potential civil or criminal penalties. (gov.uk)
Politically, the UK‑Finland engagement signals deeper defence cooperation and a coordinated regional stance through JEF. The Prime Minister’s readout also highlighted the UK’s ambition for a closer relationship with the EU-important for maintaining aligned sanctions designations, shared maritime domain awareness and consistent port‑state measures that make the shadow‑fleet model harder to sustain. (gov.uk)