The Sanctions and Money Laundering Act, external from 2018 can be used to approve the use of military force, ministers believe.
It is understood there are plans for the armed forces to use these powers, in what is being described inside government as a ramping up of action against the ships.
It is not known exactly when the first UK military action might occur.
Two oil tankers subject to US sanctions were reportedly spotted sailing east through the English Channel towards Russia on Thursday.
The UK has already imposed sanctions on more than 500 alleged shadow vessels, which it believes are helping to fund hostile activity, including Russia’s invasion of Ukraine.
Ministers say that action taken by the UK and its allies has forced around 200 ships off the seas, most of which will have been operating without a legitimate flag.
Ship flagging is the process used to register a vessel to a specific country, which then allows it to travel in international waters and offers it certain protections under law.
The government believes the new legal mechanism they have identified could be applied to any sanctioned vessels not legitimately flagged.