Officers from the Serious Organised Crime Agency (SOCA) swooped on a lorry containing around four tonnes of cannabis in a car park off Mandeville Road, Wyke Regis, yesterday morning.
It is believed to be the largest drugs bust ever to take place in West Dorset.
It was the culmination of a two-week operation after the drugs were discovered by Border Agency officials in a container heading for Dorset.
The container lorry was parked in the far corner of the car park at Value House Stores garden centre. Shocked staff told how police descended on the area.
The Dorset Police helicopter hovered over the car park as the four men, all from the Dorset area, were arrested.
One of the men was arrested just outside the garden centre's exit.
A nearby resident, who did not wish to be named, said he saw at least four police vans and four police cars at the scene.
He said: “I saw the police arrive and didn't hear any sirens.
“The police were stopping people from driving to Value House in their cars and stopping pedestrians going up there.
“All the gates were closed and I asked a man from Value House what was happening. It all seemed very hush-hush. They weren't letting anyone out of the site. We saw the police helicopter hovering over the car park.
“I went outside and saw the vans and then I saw the cars go past with what looked like the men who were arrested in them.”
It is understood that the lorry was followed after it picked up a container in which the drugs were hidden in Tilbury Docks in Essex on November 16. The container had arrived on board a ship from South Africa.
Officers swooped as the vehicle arrived at Value House stores car park yesterday morning.
The store was temporarily closed and Mandeville Road blocked while the drugs were seized and the four men arrested.
The SOCA team was assisted by officers from Dorset Police in the operation.
A spokesman for Dorset Police said: “Officers from the Serious Organised Crime Agency, assisted by units from Dorset Police, arrested four men in the area of Wyke Regis, in connection with the attempted importation of approximately four tonnes of cannabis.
“The men, all from the Dorset area, are currently being questioned at a local police station.
“The SOCA investigation was commenced on November 16, following the discovery of the drugs by officers from the UK Border Agency in Tilbury, Essex.
“The drugs, with an estimated street value of £10million, had arrived via a container shipped from South Africa.”
Value House manager Lee Mitchell said customers were given tea, coffee and biscuits while the garden centre was sealed off.
He said: “We had no knowledge or prior warning of this. There was a large amount of police in the car park and we saw people being restrained.”
SOCA tackles serious organised crime that affects the UK.
This includes Class A drugs, people smuggling and human trafficking, major gun crime, fraud, computer crime and money laundering.
SOCA officers can have the combined powers of police, customs and immigration officers.
They also have a substantial range of tools and legislation to target criminals with – everything from the ability to recover assets through to the Serious Crime Prevention Orders.
SOCA works with agencies and officials across the UK and also with organisations that stretch all over the world.