Nearly four tonnes of cocaine worth an estimated £200m was seized by law enforcement officers in the Atlantic at the start of this month.
The huge haul was found on a tugboat between the Portuguese island of Madeira and the Azores islands on 1 October.
Spanish authorities found a total 3,700 tonnes of cocaine in 165 packages on board the boat, with each package containing around 23kg of the white powder.
The National Crime Agency (NCA) said that if the haul had been cut and sold in European countries it would have fetched close to £200m. It is unclear where the drugs were being transported to.
The seven crew members were arrested by Spanish police and their ship, which bore the flag of the east African country Comoros, was towed into the port city of Cadiz on 6 October.
Six of the men are from Turkey and one is from Azerbaijan. The operation was jointly conducted by the NCA and Spanish authorities.
NCA spokesperson Mark Blackwell said: "Seizing this quantity of cocaine represents a major disruption to international crime groups, depriving them of revenue potentially running into the hundreds of millions of pounds."
So far this month, two other large drug busts have taken place in the Atlantic.
Thirteen Spanish citizens of Moroccan origin were arrested on 2 October in what officials described as the record seizure of cocaine in Morocco. Police reportedly seized more than 2.5 tonnes of cocaine, which has a street value of hundreds of millions of dollars.
The drugs are believed to have come from Venezuela, with Morocco's investigations chief Abdelhak Khiam saying that South American cartels were using smuggling routes through North Africa due to the region's "lack of control" on drug trafficking.
On 5 October, the Portuguese navy intercepted a boat transporting cocaine to the country from the Caribbean.
The boat was carrying a large amount of "highly pure" cocaine with an estimated worth of around £18m, Portugal News Online reported.