Nearly 1.3 tonnes of heroin with a street value of £120m has been found in what is thought to be the UK's largest ever seizure of the drug.
The drugs were found concealed in towels and bathrobes on a container ship after it docked in Suffolk.
National Crime Agency (NCA) officers removed the drugs and returned the container before tracking it to the Netherlands and making arrests.
The ship docked in Felixstowe, where it was intercepted by the NCA.
It came in the month £40m of heroin, about 400kg (62st 13lb), was found in similar circumstances at Felixstowe dock on 2 August.
In the latest seizure, blocks of heroin - each weighing 1kg (2.2lb) - were found stitched inside some of the towels, and it took Border Force officers six hours to remove all of the drugs, weighing a total of 1,297kg (204st).
After taking the drugs out on 30 August, officers put the container back on to the ship, which continued on to its destination in Antwerp where it docked two days later.
The container was then driven by lorry to a warehouse in the Dutch port city of Rotterdam, where upon arrival officers arrested four men in the process of unloading it.
BBC home affairs correspondent Danny Shaw said the drugs had originated in Pakistan.
NCA deputy director of investigations, Matt Horne, called the haul "a record heroin seizure in the UK and one of the largest ever in Europe".
He said: "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.
"The heroin trade also feeds addictions that put users' lives at risk, while giving rise to crime such as theft which make people feel unsafe in their homes and communities."