Heroin with a street value of more than £120 million has been discovered hidden among towels and dressing gowns on board a container ship.
The haul - weighing nearly 1.3 tonnes - is the largest ever seizure of the Class A drug in the UK.
National Crime Agency (NCA) officers took six hours to remove the haul after the container ship docked in Felixstowe on Friday.
Heroin blocks were found stitched inside some of the towels.
The drugs were removed and the ship was tracked by officials to Belgium and the Netherlands, where officers swooped in and made arrests.
NCA deputy director, investigations, Matt Horne, said: “This is a record heroin seizure in the UK and one of the largest ever in Europe.
“The size of this and other recent shipments demonstrate the scale of the threat we face.
“We can be certain that some of these drugs would eventually have been sold in the UK, fuelling high levels of violence and exploitation including what we see in county lines offending nationwide.”
Video footage of the seizure showed the drugs stored in packets labelled as protein powder, which were inside boxes filled with towels and dressing gowns.
Intelligence had determined the drugs would be on board the ship, as it docked in the UK en-route to Belgium.
Officers found 1,297kg of heroin inside when it arrived in Felixstowe and after the drugs had been removed, the container was returned to the ship and it was tracked to Antwerp, Belgium on September 1.
The container was kept under surveillance and was driven by lorry to a warehouse in Rotterdam in the Netherlands.
Officers swooped in and arrested four people as they unloaded the container.
The latest seizure comes after officers discovered 398kg of heroin on a vessel at Felixstowe port on August 2.
Jenny Sharp, Border Force assistant director at Felixstowe, said: “This is a huge seizure, there is no other word for it given the quantities involved, which has kept dangerous drugs off the streets of the UK and mainland Europe.
“The smugglers had hidden the drugs within a cover load of towels, stitching the 1kg blocks of heroin inside some of the towels.
“In total it took my officers nearly six hours, working in the early hours of Saturday morning, to remove the drugs.”