The geared general cargo vessel, flying the flag of the Netherlands Antilles, was said to be carrying Russian Mi25 attack helicopters known as "flying tanks" and stopped under the terms of the European Union arms embargo against the Syrian government.
The insurance was withdrawn on the grounds of "broken internal rules" of the club. The London-based insurer told BBC News it was under no pressure from the British government.
British Foreign Secretary William Hague in a recent meeting with Russian Foreign Minister Lavrov demanded that all defence shipments to Syria stop.
"We are working closely with international partners to ensure that we are doing all we can to stop the Syrian regime's ability to slaughter civilians being reinforced through assistance from other countries," Mr Hague added.