Police have seized £120m worth of heroin that was hidden inside bags of rice.
The drugs were found in a container ship at the port of Felixstowe, in Suffolk, on Sunday.
Authorities then returned the “Sembawang” ship under surveillance as part of an international operation.
It sailed to Antwerp in Belgium where it docked on Tuesday and the container was driven by lorry to a warehouse south of The Hague in the Netherlands.
Upon arrival, officers moved in and arrested three people – the driver and two men involved in the unloading.
As they were arrested, a 45-year-old man who is suspected to be a UK facilitator in the organised crime group was detained on the M40 by Thames Valley Police assisting the National Crime Agency (NCA).
He has been released on bail.
The 1,196kg of heroin and morphine derivatives would be worth around £21 million to organised criminals at wholesale and in excess of £120 million at street level, the NCA said.
Heroin is typically supplied via county lines dealing, which relies on the exploitation of children and vulnerable people to transport the drugs.
The NCA said the seizure is one of the largest ever of heroin in the UK.
Nikki Holland, NCA director of investigations, said: “This is a huge seizure which has denied organised criminals tens of millions of pounds in profits, and is the result of a targeted, intelligence-led investigation carried out by the NCA with international and UK partners.”
Minister for immigration compliance and courts Chris Philp added: “Even though the container ship was destined for the Netherlands, it is highly likely its illicit cargo could have ended up on UK streets as well as mainland Europe.
“Class A drugs like heroin and diamorphine wreak havoc on individuals and communities, and there is no place for them in any civilised society.”