According to tracking website MarineTraffic, Smyrtos sails under a Cameroon flag.
It began its journey on 5 June from Russia’s Ust-Luga port, an oil terminal near St Petersburg, before crossing west into the Channel on Saturday, BBC Verify has found.
The vessel was sanctioned in July 2025 and has since changed its name from Myrtos to Smyrtos as well as the flag it sails under twice.
The MoD said the operation had happened in international waters as it was more than 12 nautical miles from the UK coast.
It said it had been in full compliance with both domestic and international law.
The interception was the result of weeks of military and political planning, an MoD spokesman said.
It was conducted in close co-ordination with the French, the MoD said, building on recent support provided by the UK to its allies.
French President Emmanuel Macron said on 1 June that his country’s military had intercepted a sanctioned oil tanker suspected of being part of the “shadow fleet” with UK support.
A British helicopter provided support during that operation, the MoD told the BBC.
