Spanish police today found more than three tons of cocaine with an estimated street value of Stg£122 million on a British-flagged ship.
British Customs officials helped police with the pre-dawn raid on the vessel, the Gibraltar-registered
Barthon Queen
.
Much of the consignment could eventually have found its way into Britain, a Customs and Excise spokesman said.
The ship was about 2,400 miles south of the Canary Islands and 11 miles from the coast of the African nation of Togo.
Seven people, including four from Chile and one each from Portugal, the Netherlands and France, were arrested.
The Customs spokesman said: "We are delighted to have been able to give some assistance to the Spanish authorities in taking out these drugs.
"The Spanish had to get our permission to board the ship, as it was in international waters and officially UK registered."
He added: "Spain is the drugs gateway to Europe from South America and a lot of these drugs could have ended up in Britain."
Customs had been watching the vessel when it docked in Gibraltar late last year.
The ship then sailed to an unspecified place in the southern Atlantic to pick up the cocaine, which came from Colombia, Spanish customs officials said.
In February, Spanish police seized more than five tons of cocaine on a British ship near the Canary Islands in their biggest haul so far this year.