Prime Minister Keir Starmer's government announced that British armed forces and law enforcement officers would be able to interdict vessels sanctioned by the United Kingdom while those ships transit UK waters, including the English Channel, in a Prime Minister's Office news release timed 25 March 2026.
The policy targets Russia's shadow fleet of tankers and related ships that Western governments say help move oil outside normal insurance and ownership scrutiny, tightening a maritime choke point London shares with busy allied routes.
Downing Street said each target ship would be individually considered by law enforcement, military, and energy market specialists before ministers received a recommendation and any operation ran, and it noted criminal proceedings could follow detention.
What ministers said they were changing at sea
The published notice said the Prime Minister had agreed that UK Armed Forces and law enforcement could now interdict UK-sanctioned vessels transiting UK waters.
It described the step as the latest blow to a shadow fleet fuelling Russia's war in Ukraine.
The same text said Royal Navy units had recently supported allies monitoring and tracking several shadow fleet ships so partners could interdict them in European and Mediterranean waters.
It pointed to Finnish, Swedish, and Estonian operations in the Baltic as part of a Joint Expeditionary Force effort Starmer was joining in Helsinki.
The release also said ministers had ordered plans after a successful United States seizure of the tanker Bella 1, which UK assets supported.
It stated that alongside allies the United Kingdom had imposed sanctions on 544 Russian shadow fleet vessels while claiming about 75 percent of Russia's crude oil moved on that fleet.
That's why we're going after his shadow fleet even harder, not just keeping Britain safe but starving Putin's war machine of the dirty profits that fund his barbaric campaign in Ukraine.
The sentence appeared in a longer statement under Starmer's name in the 25 March 2026 Prime Minister's Office publication.
What AIS-based monitoring recorded after the authorisation
BBC Verify, in ship-tracking analysis dated 12 May 2026, said it matched automatic identification system data from MarineTraffic to ships appearing on the Foreign, Commonwealth and Development Office sanctions list.
It reported 184 UK-sanctioned vessels making 238 journeys through UK waters between 00:00 on 25 March and 15:00 British Summer Time on 11 May.
The same article said most journeys crossed the English Channel and that each ship entered the United Kingdom's exclusive economic zone reaching out to 200 nautical miles from the coast.
It added that in at least 94 instances a ship briefly entered territorial waters extending to 12 nautical miles.
BBC Verify wrote that the government had not publicly stated or offered evidence that any of those ships had been boarded.
It said the Ministry of Defence did not answer its direct question on that point while stating the armed forces were disrupting and deterring shadow fleet vessels.
The article also said the ministry reported more than 700 suspected vessels challenged since October 2024 but did not define challenged when asked again.
Voices on law, risk, and credibility at sea
Tom Sharpe, identified as a former Royal Navy warship commander, told BBC Verify it had been utterly confusing and pathetic that no boardings had been carried out despite available warships and boarding teams.
James M Turner KC, a shipping lawyer at Quadrant Chambers, told BBC Verify that with very few exceptions a coastal state cannot seize a vessel that is flying a flag it is entitled to fly.
He said that left very little room to act regardless of sanctions status unless a ship was falsely flagged or had no flag.
BBC Verify said the oil tanker Yi Tong, which it said was registered to the Chinese company Pacific Shipmanagement in Shandong, took a longer route around Ireland and northern Scotland in April 2026 after previously using the English Channel between Russia and China.
Alessio Patalano, professor of war and strategy at King's College London, told BBC Verify that such rerouting suggested the policy could still impose cost through extra fuel and time even when tankers were not seized.
Downing Street's March text said operators would face longer, financially painful routes or risk detention, and it repeated that specialists would weigh each case before ministers approved an operation.