Global law firm Reed Smith has said Gibraltar's seizure of a VLCC in an alleged sanctions breach should serve as a warning to others.

Leigh Hansson, a partner in its global regulatory enforcement group, said: “The UK’s seizure of an Iranian oil tanker bound for Syria is a reminder of the broad reach of both US and EU sanctions regimes."

The 301,000-dwt Ukrainian-owned Grace 1 (built 1997) was detained by British marines in the territory on 4 July.

It was alleged to be carrying Iranian oil to Syria, which would place it in breach of both US and EU regimes.

Hansson, who is also a leading lawyer in the firm’s international trade and national security team, said: "Given that Iran is not a member of the EU, it might seem flawed to cite Iran as having fallen foul of EU sanctions.

"However, the vessel was seized off the coast of Gibraltar which, as a British overseas territory, is part of the EU, so EU sanctions would indeed apply."

She added: “This event should act as a stark warning to businesses and organisations seeking to continue their operations with regions that are currently subjected to sanctions: sanctions apply and are being enforced even in areas that may not seem immediately obvious.

"It is advisable to consider carefully whether any planned activities linked to sanctioned regions might be construed as infringements of an extensive and well-policed regime.”